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ientific skepticism secular humanism secularism organizations camp quest american atheists atheist foundation of australia freedom from religion foundation rationalist international internet infidels fellowship of reason society of the godless satire apatheism evil atheist conspiracy flying spaghetti monster invisible pink unicorn external links web sites associations atheist alliance international american atheists freedom from religion foundation atheist foundation of australia the national secular society uk the brights idaho atheists web communities frostcloud com discuss atheism atheist parents group booktalk org the freethinker s book discussion community church of reality freethinkers nobeliefs com positive atheism the secular web the atheist coalition the faithless community eudaimonist s euphoria internet radios atheist network internet radio the infidel guy radio show freethought radio internet radio station miscellaneous ebon musings the atheism pages exchristian net encouraging ex christians links |
related to atheism by atheists of silicon valley political and atheist thought camp quest a secular summer camp for children darwin bedford atheist messiah and spiritual reality therapist religioustolerance org http www qsmithwmu com web site of quentin smith atheist philosopher http www abstractatom com web site of jeffrey grupp atheist philosopher articles history of a historical outline of modern religious criticism in western civilization history of atheistic thought going back to the one five zero zero s definitions allrefer atheism article brief discussion of polemical usage atheism and agnosticism by john smart for stanford encyclopedia of philosophy definition of atheism from atheist foundation of australia inc types of atheistic belief what is atheism from positive atheism magazine defence the end of faith by sam harris atheism defended atheism the capital man introduction to a contribution to the critique of hegel s philosophy of right the source of the famous religion is the opiate of the masses b |
y karl marx lecture on atheism by erkki hartikainen in the finnish society for natural philosophy two zero zero three the philosophy of atheism by emma goldman mother earth one nine one six why atheism an atheist manifesto by sam harris criticism catholic encyclopedia atheism the twilight of atheism by alister mcgrath christianity today march two zero zero five theism atheism and rationality by alvin plantinga intellectual sophistication and basic belief in god by alvin plantinga statistics atheism contemporary rates and patterns atheism worldwide by phil zuckerman references altizer thomas j j one nine six seven the gospel of christian atheism london collins electronic text armstrong karen one nine nine nine a history of god london vintage isbn zero zero nine nine two seven three six seven five ayer a j one nine six six what i believe in humanist vol eight one eight august one nine six six p two two six two two eight baggini julian two zero zero three atheism a very short introduction oxford oxford universit |
y press isbn zero one nine two eight zero four two four three berman david one nine nine zero a history of atheism in britain from hobbes to russell london routledge isbn zero four one five zero four seven two seven seven berman david one nine eight three david hume and the suppression of atheism in journal of the history of philosophy vol two one three july one nine eight three p three seven five three eight seven berman david one nine eight two the repressive denials of atheism in britain in the seventeenth and eighteenth centuries in proceedings of the royal irish academy vol eight two c nine p two one one two four six borne tienne one nine six one atheism new york hawthorn books originally published in france under the title dieu n est pas mort essai sur l atheisme contemporain librairie arth me fayard one nine five nine bradlaugh bonner hypatia one nine zero eight charles bradlaugh a record of his life and work london t fisher unwin buckley m j one nine eight seven at the origins of modern atheism new ha |
ven ct yale university press cudworth ralph one six seven eight the true intellectual system of the universe the first part wherein all the reason and philosophy of atheism is confuted and its impossibility demonstrated d holbach p h t one seven seven two good sense electronic text d holbach p h t one seven seven zero the system of nature electronic versions complete text pdf complete text html de mornay phillipe one five eight seven a woorke concerning the trewnesse of the christian religion written in french against atheists epicures paynims iewes mahumetists london drachmann a b one nine two two atheism in pagan antiquity chicago ares publishers one nine seven seven an unchanged reprint of the one nine two two edition isbn zero eight nine zero zero five two zero one eight everitt nicholas two zero zero four the non existence of god an introduction london routledge isbn zero four one five three zero one zero seven six evolution and religion can coexist scientists say flew antony one nine six six god and phi |
losophy london hutchinson co flew antony one nine eight four a god freedom and immortality a critical analysis buffalo ny prometheus isbn zero eight seven nine seven five one two seven four flew antony one nine eight four b the presumption of atheism new york prometheus complete text html flew antony one nine seven two the presumption of atheism in canadian journal of philosophy two p two nine four six reprinted in flew one nine eight four a and one nine eight four b above flint robert one eight seven seven anti theistic theories being the baird lecture for one eight seven seven london william blackwood and sons five th ed one eight nine four gaskin j c a ed one nine eight nine varieties of unbelief from epicurus to sartre new york macmillan isbn zero zero two three four zero six eight one x harbour daniel two zero zero one an intelligent person s guide to atheism london duckworth isbn zero seven one five six three two two nine nine hitchens christopher two zero zero one letters to a young contrarian new york |
basic books krueger d e one nine nine eight what is atheism a short introduction new york prometheus isbn one five seven three nine two two one four five le poidevin r one nine nine six arguing for atheism an introduction to the philosophy of religion london routledge isbn zero four one five zero nine three three eight four levin s one nine nine five jewish atheism in new humanist vol one one zero two may one nine nine five p one three one five lyas colin one nine seven zero on the coherence of christian atheism in philosophy the journal of the royal institute of philosophy vol four five one seven one january one nine seven zero pp one one nine mackie j l one nine eight two the miracle of theism arguments for and against the existence of god oxford oxford university press isbn zero one nine eight two four six eight two x maritain jacques one nine five three the range of reason london geoffrey bles electronic text note chapter eight the meaning of contemporary atheism p one zero three one one seven electronic |
text is reprinted from review of politics vol one one three july one nine four nine p two six seven two eight zero electronic text a version also appears the listener vol four three no one one zero two nine march one nine five zero pp four two seven four two nine four three two martin michael one nine nine zero atheism a philosophical justification philadelphia pa temple university press isbn zero eight seven seven two two nine four three zero martin michael monnier r eds two zero zero three the impossibility of god new york prometheus mcgrath a two zero zero five the twilight of atheism the rise and fall of disbelief in the modern world isbn zero three eight five five zero zero six two nine mctaggart john mctaggart ellis one nine two seven the nature of existence volume two cambridge cambridge university press mctaggart john mctaggart ellis one nine three zero some dogmas of religion london edward arnold co new edition first published one nine zero six mills d two zero zero four atheist universe xlibris isb |
n one four one three four three four eight one nine m ller f max one eight eight nine natural religion the gifford lectures one eight eight eight london longmans green and co nagel ernest one nine six five a defence of atheism in edwards paul and pap arthur eds a modern introduction to philosophy readings from classical and contemporary sources new york free press rev ed pp four six zero four seven two nielsen kai one nine eight five philosophy and atheism new york prometheus isbn zero eight seven nine seven five two eight nine zero nielsen kai two zero zero one naturalism and religion new york prometheus reid j p one nine six seven atheism in new catholic encyclopedia new york mcgraw hill p one zero zero zero one zero zero three rizzuto ana maria one nine nine eight why did freud reject god a psychoanalytic interpretation yale university press isbn zero three zero zero zero seven five two five one robinson richard one nine six four an atheist s values oxford clarendon press sharpe r a one nine nine seven the |
moral case against religious belief london scm press isbn zero three three four zero two six eight zero six smith george h one nine nine zero atheism ayn rand and other heresies new york prometheus excerpt defining atheism html smith george h one nine seven nine atheism the case against god buffalo new york prometheus isbn zero eight seven nine seven five one two four x excerpt the scope of atheism html sobel jordan h two zero zero four logic and theism arguments for and against beliefs in god cambridge cambridge university press stenger victor j two zero zero three has science found god new york prometheus stein g ed one nine eight four the encyclopaedia of unbelief vols one two new york prometheus isbn zero eight seven nine seven five three zero seven two thrower james one nine seven one a short history of western atheism london pemberton isbn zero three zero one seven one one zero one one vitz paul one nine nine nine faith of the fatherless the psychology of atheism dallas texas spence isbn one eight nine |
zero six two six one two zero atheism philosophy of religion agnosticism is the philosophical view that the truth or falsity of certain claims particularly theological claims regarding the existence of god or gods is unknown unknowable or incoherent some agnostics infer from this that these claims are irrelevant to life the term and the related agnostic were coined by thomas henry huxley in one eight six nine and are also used to describe those who are unconvinced or noncommittal about the existence of deities as well as other matters of religion the word agnostic comes from the greek a without and gnosis knowledge agnosticism focusing on what can be known is an epistemological position dealing with the nature and limits of human knowledge while atheism and theism are ontological positions a branch of metaphysics that deals with what types of entities exist agnosticism is not to be confused with a view specifically opposing the doctrine of gnosis and gnosticism these are religious concepts that are not gener |
ally related to agnosticism agnosticism is distinct from strong atheism also called positive atheism or dogmatic atheism which denies the existence of any deities however the more general variety of atheism weak atheism also called negative atheism and sometimes neutral atheism professes only a lack of belief in a god or gods which is not equivalent to but is compatible with agnosticism critical atheism admits that a god or gods are meaningful concepts but the evidence for them is not in hand so a default position of not believing in them must be taken in the interim agnostics may claim that it isn t possible to have absolute or certain spiritual knowledge or alternatively that while certainty may be possible they personally have no such knowledge in both cases agnosticism involves some form of skepticism towards religious statements this is different from the simple irreligion of those who give no thought to the subject variations agnosticism has suffered more than most expressions of philosophical position |
from terminological vagaries data collection services often display the common use of the term distinct from strong atheism in its lack of disputing the existence of deities agnostics are listed alongside secular non religious or other such categories other variations include strong agnosticism also called hard agnosticism closed agnosticism strict agnosticism absolute agnosticism the view that the question of the existence of deities is unknowable by nature or that human beings are ill equipped to judge the evidence weak agnosticism also called soft agnosticism open agnosticism empirical agnosticism temporal agnosticism the view that the existence or nonexistence of god or gods is currently unknown but isn t necessarily unknowable therefore one will withhold judgment until more evidence is available apathetic agnosticism the view that there is no proof either of god s existence or nonexistence but since god if there is one appears unconcerned for the universe or the welfare of its inhabitants the question is |
largely academic ignosticism the view that the concept of god as a being is meaningless because it has no verifiable consequences therefore it cannot be usefully discussed as having existence or nonexistence see scientific method model agnosticism the view that philosophical and metaphysical questions are not ultimately verifiable but that a model of malleable assumption should be built upon rational thought this branch of agnosticism does not focus on a deity s existence agnostic theism the view of those who do not claim to know god s existence but still believe in his existence see knowledge vs beliefs whether this is truly agnosticism is disputed it may also imply the belief that although there is something that resembles or would at least appear to us as a god or gods there remains doubt over their true nature motives or the validity of the claim to be god rather than superior supernatural being s agnostic spiritualism the view that there may or may not be a god or gods while maintaining a general person |
al belief in a spiritual aspect of reality particularly without distinct religious basis or adherence to any established doctrine or dogma agnostic atheism the view that god may or may not exist but that his non existence is more likely some agnostic atheists would at least partially base their beliefs on occam s razor some philosophical opinions among the most famous agnostics in the original sense have been robert g ingersoll thomas henry huxley and charles darwin some have argued from the works of david hume especially dialogues concerning natural religion that he was an agnostic but this remains subject to debate thomas henry huxley agnostic views are as old as philosophical skepticism but the terms agnostic and agnosticism were created by huxley to sum up his thoughts on contemporary developments of metaphysics about the unconditioned hamilton and the unknowable herbert spencer it is important therefore to discover huxley s own views on the matter though huxley began to use the term agnostic in one eight |
six nine his opinions had taken shape some time before that date in a letter of september two three one eight six zero to charles kingsley huxley discussed his views extensively i neither affirm nor deny the immortality of man i see no reason for believing it but on the other hand i have no means of disproving it i have no a priori objections to the doctrine no man who has to deal daily and hourly with nature can trouble himself about a priori difficulties give me such evidence as would justify me in believing in anything else and i will believe that why should i not it is not half so wonderful as the conservation of force or the indestructibility of matter it is no use to talk to me of analogies and probabilities i know what i mean when i say i believe in the law of the inverse squares and i will not rest my life and my hopes upon weaker convictions that my personality is the surest thing i know may be true but the attempt to conceive what it is leads me into mere verbal subtleties i have champed up all tha |
t chaff about the ego and the non ego noumena and phenomena and all the rest of it too often not to know that in attempting even to think of these questions the human intellect flounders at once out of its depth and again to the same correspondent may six one eight six three i have never had the least sympathy with the a priori reasons against orthodoxy and i have by nature and disposition the greatest possible antipathy to all the atheistic and infidel school nevertheless i know that i am in spite of myself exactly what the christian would call and so far as i can see is justified in calling atheist and infidel i cannot see one shadow or tittle of evidence that the great unknown underlying the phenomenon of the universe stands to us in the relation of a father who loves us and cares for us as christianity asserts so with regard to the other great christian dogmas immortality of soul and future state of rewards and punishments what possible objection can i who am compelled perforce to believe in the immortali |
ty of what we call matter and force and in a very unmistakable present state of rewards and punishments for our deeds have to these doctrines give me a scintilla of evidence and i am ready to jump at them of the origin of the name agnostic to describe this attitude huxley gave coll ess v pp two three seven two three nine the following account so i took thought and invented what i conceived to be the appropriate title of agnostic it came into my head as suggestively antithetic to the gnostic of church history who professed to know so much about the very things of which i was ignorant to my great satisfaction the term took huxley s agnosticism is believed to be a natural consequence of the intellectual and philosophical conditions of the one eight six zero s when clerical intolerance was trying to suppress scientific discoveries which appeared to clash with a literal reading of the book of genesis and other established jewish and christian doctrines agnosticism should not however be confused with natural theolo |
gy deism pantheism or other science positive forms of theism by way of clarification huxley states in matters of the intellect follow your reason as far as it will take you without regard to any other consideration and negatively in matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable huxley agnosticism one eight eight nine while a w momerie has noted that this is nothing but a definition of honesty huxley s usual definition goes beyond mere honesty to insist that these metaphysical issues are fundamentally unknowable bertrand russell bertrand russell s pamphlet why i am not a christian based on a speech delivered in one nine two seven and later included in a book of the same title is considered a classic statement of agnosticism the essay briefly lays out russell s objections to some of the arguments for the existence of god before discussing his moral objections to christian teachings he then calls upon his readers to stand on their own two feet and |
look fair and square at the world with a fearless attitude and a free intelligence in one nine three nine russell gave a lecture on the existence and nature of god in which he characterised himself as an agnostic he said the existence and nature of god is a subject of which i can discuss only half if one arrives at a negative conclusion concerning the first part of the question the second part of the question does not arise and my position as you may have gathered is a negative one on this matter collected papers vol one zero p two five five however later in the same lecture discussing modern non anthropomorphic concepts of god russell states that sort of god is i think not one that can actually be disproved as i think the omnipotent and benevolent creator can p two five eight in russell s one nine four seven pamphlet am i an atheist or an agnostic subtitled a plea for tolerance in the face of new dogmas he ruminates on the problem of what to call himself as a philosopher if i were speaking to a purely philo |
sophic audience i should say that i ought to describe myself as an agnostic because i do not think that there is a conclusive argument by which one prove that there is not a god on the other hand if i am to convey the right impression to the ordinary man in the street i think i ought to say that i am an atheist because when i say that i cannot prove that there is not a god i ought to add equally that i cannot prove that there are not the homeric gods in his one nine five three essay what is an agnostic russell states an agnostic thinks it impossible to know the truth in matters such as god and the future life with which christianity and other religions are concerned or if not impossible at least impossible at the present time however later in the essay russell says i think that if i heard a voice from the sky predicting all that was going to happen to me during the next twenty four hours including events that would have seemed highly improbable and if all these events then produced to happen i might perhaps b |
e convinced at least of the existence of some superhuman intelligence he didn t say supreme or supernatural intelligence these terms are metaphysically loaded for russell then agnosticism doesn t necessarily assert that it is in principle impossible to know whether or not there is a god moreover an agnostic may think the christian god as improbable as the olympians in that case he is for practical purposes at one with the atheists logical positivism logical positivists such as rudolph carnap and a j ayer are sometimes thought to be agnostic using arguments reminiscent of wittgenstein s famous whereof one cannot speak thereof one must be silent they viewed any talk of god s as literally nonsense for the logical positivists and adherents of similar schools of thought statements about religious or other transcendent experiences could not have a truth value and were deemed to be without meaning but this includes all utterances about god s even those agnostic statements that deny knowledge of god s are possible in |
language truth and logic ayer explicitly rejects agnosticism on the grounds that an agnostic despite claiming that knowledge of god s are not possible nevertheless holds that statements about god s have meaning this position however is valid only in the case of agnostics who define their agnosticism in this fashion ignostics define agnosticism in a manner consistent with the logical positivist view holding theism to be incoherent references collected essays thomas huxley isbn one eight five five zero six nine two two nine man s place in nature thomas huxley isbn zero three seven five seven five eight four seven x why i am not a christian bertrand russell isbn zero six seven one two zero three two three one dialogues concerning natural religion david hume isbn zero one four zero four four five three six six language truth and logic a j ayer isbn zero four eight six two zero zero one zero eight see also list of agnostics religious freedom external links what is an agnostic by bertrand russell one nine five thr |
ee dictionary of the history of ideas agnosticism the internet infidels discussion forums worldwide the secular web stanford encyclopedia of philosophy entry religious tolerance org agnosticism agnostic agnosticism and christianity one eight nine nine by t h huxley agnosis the history future of agnosticism agnosticism argon is a chemical element in the periodic table it has the symbol ar and atomic number one eight the third noble gas in group one eight argon makes up about one of the earth s atmosphere making it the most common noble gas on earth notable characteristics argon is two five times as soluble in water as nitrogen which is approximately the same solubility as oxygen this highly stable chemical element is colorless and odorless in both its liquid and gaseous forms there are few known true chemical compounds that contain argon which is one of the reasons it was formerly called an inert gas the creation of argon hydrofluoride harf a highly unstable compound of argon with fluorine was reported by rese |
archers at the university of helsinki in two zero zero zero but has not been confirmed as of yet although no chemical compounds of argon are presently confirmed argon can form clathrates with water when atoms of it are trapped in a lattice of the water molecules theoretical calculations on computers have shown several argon compounds that should be stable but for which no synthesis routes are currently known applications it is used in lighting since it will not react with the filament in a lightbulb even under high temperatures and other cases where diatomic nitrogen is an unsuitable semi inert gas other uses argon is used as an inert gas shield in many forms of welding including mig and tig where the i stands for inert as a non reactive blanket in the manufacture of titanium and other reactive elements as a protective atmosphere for growing silicon and germanium crystals as a gas for use in plasma globes as a gas for use in energy efficient windows argon three nine has been used for a number of applications |
primarily ice coring it has also been used for ground water dating cryosurgery procedures such as cryoablation uses liquefied argon to destroy cancer cells argon is also used in technical scuba diving to inflate the dry suit because it is inert and has low thermal conductivity history argon greek argos meaning inactive was suspected to be present in air by henry cavendish in one seven eight five but was not discovered until one eight nine four by lord rayleigh and sir william ramsay occurrence this gas is isolated through liquid air fractionation since the atmosphere contains only zero nine three four volume of argon one two nine mass the martian atmosphere in contrast contains one six of ar four zero and five ppm ar three six in two zero zero five the huygens probe also discovered the presence of ar four zero on titan the largest moon of saturn compounds before one nine six two argon and the other noble gases were generally considered to be chemically inert and not able to form compounds however since then s |
cientists have been able to force the heavier noble gases to form compounds in two zero zero zero the first argon compounds were formed by researchers at the university of helsinki by shining ultraviolet light onto frozen argon containing a small amount of hydrogen fluoride they were able to form argon hydrofluoride harf see http pubs acs org cen eight zero th noblegases html in its paragraph starting many recent findings it is stable up to four zero k isotopes the main isotopes of argon found on earth are ar four zero ar three six and ar three eight naturally occurring k four zero with a half life of one two five zero x one zero nine years decays to stable ar four zero one one two by electron capture and by positron emission and also transforms to stable ca four zero eight eight eight via beta decay these properties and ratios are used to determine the age of rocks in the earth s atmosphere ar three nine is made by cosmic ray activity primarily with ar four zero in the subsurface environment it is also produ |
ced through neutron capture by k three nine or alpha emission by calcium argon three seven is created from the decay of calcium four zero as a result of subsurface nuclear explosions it has a half life of three five days references los alamos national laboratory argon external links webelements com argon diving applications why argon argon ar properties uses applications computational chemistry wiki chemical elements noble gases arsenic is a chemical element in the periodic table that has the symbol as and atomic number three three this is a notoriously poisonous metalloid that has three allotropic forms yellow black and grey arsenic and its compounds are used as pesticides herbicides insecticides and various alloys notable characteristics arsenic is very similar chemically to its predecessor phosphorus so much so that it will partly substitute for phosphorus in biochemical reactions and is thus poisonous when heated it rapidly oxidizes to arsenic trioxide which has a garlic odor arsenic and some arsenic comp |
ounds can also sublime upon heating converting directly to a gaseous form elemental arsenic is found in two solid forms yellow and gray metallic with specific gravities of one nine seven and five seven three respectively applications lead hydrogen arsenate has been used well into the two zero th century as an insecticide on fruit trees resulting in neurological damage to those working the sprayers and scheele s green has even been recorded in the one nine th century as a coloring agent in sweets in the last half century monosodium methyl arsenate msma a less toxic organic form of arsenic has replaced lead arsenate s role in agriculture the application of most concern to the general public is probably that of wood which has been treated with chromated copper arsenate cca or tanalith and the vast majority of older pressure treated wood cca timber is still in widespread use in many countries and was heavily used during the latter half of the two zero th century as a structural and outdoor building material where |
there was a risk of rot or insect infestation in untreated timber although widespread bans followed the publication of studies which showed low level leaching from in situ timbers such as children s playground equipment into surrounding soil the most serious risk is presented by the burning of cca timber recent years have seen fatal animal poisonings and serious human poisonings resulting from the ingestion directly or indirectly of wood ash from cca timber the lethal human dose is approximately two zero grams of ash roughly a tablespoon scrap cca construction timber continues to be widely burnt through ignorance in both commercial and domestic fires safe disposal of cca timber remains patchy and little practiced there is concern in some quarters about the widespread landfill disposal of such timber during the one eight th one nine th and two zero th centuries a number of arsenic compounds have been used as medicines including arsphenamine by paul ehrlich and arsenic trioxide by thomas fowler arsphenamine as |
well as neosalvarsan was indicated for syphilis and trypanosomiasis but has been superseded by modern antibiotics arsenic trioxide has been used in a variety of ways over the past two zero zero years but most commonly in the treatment of cancer the fda in two zero zero zero approved this compound for the treatment of patients with acute promyelocytic leukemia that is resistant to atra but arsenic isn t always good for cancer some studies show that if you use arsenic you have a high risk for cancer copper acetoarsenite was used as a green pigment known under many different names including paris green and emerald green it caused numerous arsenic poisonings other uses various agricultural insecticides and poisons gallium arsenide is an important semiconductor material used in integrated circuits circuits made using the compound are much faster but also much more expensive than those made in silicon unlike silicon it is direct bandgap and so can be used in laser diodes and leds to directly convert electricity in |
to light arsenic trioxide is used in australia for treating termite infestations in houses also used in bronzing and pyrotechny history the word arsenic is borrowed from the persian word zarnikh meaning yellow orpiment zarnikh was borrowed by greek as arsenikon arsenic has been known and used in persia and elsewhere since ancient times as the symptoms of arsenic poisoning were somewhat ill defined it was frequently used for murder until the advent of the marsh test a sensitive chemical test for its presence another less sensitive but more general test is the reinsch test due to its use by the ruling class to bump each other off and its incredible potency and discreetness arsenic has been called the poison of kings and the king of poisons during the bronze age arsenic was often included in the bronze mostly as an impurity which made the alloy harder albertus magnus is believed to have been the first to isolate the element in one two five zero in one six four nine johann schroeder published two ways of preparin |
g arsenic alchemical symbol for arsenicthe alchemical symbol for arsenic is shown opposite in victorian times arsenic was mixed with vinegar and chalk and eaten by women to improve the complexion of their faces making their skin more fair to show they did not work in the fields arsenic was also rubbed into the faces and arms of women to improve their complexion there is a massive epidemic of arsenic poisoning in bangladesh where it is estimated that approximately five seven million people are drinking groundwater with arsenic concentrations elevated above the world health organization s standard of five zero parts per billion the arsenic in the groundwater is of natural origin and is released from the sediment into the groundwater due to the anoxic conditions of the subsurface this groundwater began to be used after western ngos instigated a massive tube well drinking water program in the late twentieth century this program was designed to prevent drinking of bacterially contaminated surface waters but unfort |
unately failed to test for arsenic in the groundwater two many other countries in south east asia such as vietnam cambodia and tibet are thought to have geological environments similarly conducive to generation of high arsenic groundwaters occurrence massive native arsenic arsenopyrite also called mispickel fesas is the most common mineral from which on heating the arsenic sublimes leaving ferrous sulfide other arsenic minerals include realgar mimetite cobaltite and erythrite the most important compounds of arsenic are white arsenic its sulfide paris green calcium arsenate and lead hydrogen arsenate paris green calcium arsenate and lead arsenate have been used as agricultural insecticides and poisons it is sometimes found native but usually combined with silver cobalt nickel iron antimony or sulfur in addition to the inorganic forms mentioned above arsenic also occurs in various organic forms in the environment inorganic arsenic and its compounds upon entering the food chain are progressively metabolised to a |
less toxic form of arsenic through a process of methylation precautions arsenic and many of its compounds are especially potent poisons arsenic kills by allosteric inhibition of the metabolic enzyme lipothiamide pyrophosphate leading to death from multi system organ failure see arsenic poisoning arsenic and its compounds inhibit the which is an important enzyme of metabolism the post mortem reveals brick red colored mucosa due to severe haemorrhage elemental arsenic and arsenic compounds are classified as toxic and dangerous for the environment in the european union under directive six seven five four eight eec the iarc recognizes arsenic and arsenic compounds as group one carcinogens and the eu lists arsenic trioxide arsenic pentoxide and arsenate salts as category one carcinogens growing the brake fern pteris vittata will remove arsenic from the soil see also aqua tofana fowler s solution arsenicosis compounds arsenic acid h three aso four arsenous acid h three aso three arsenic trioxide as two o three ars |
ine arsenic trihydride ash three cadmium arsenide cd three as two gallium arsenide gaas lead hydrogen arsenate pbhaso four see also references los alamos national laboratory arsenic endnotes antman karen h two zero zero one the history of arsenic trioxide in cancer therapy introduction to a supplement to the oncologist six suppl two one two pmid one one three three one four three three andrew meharg venomous earth how arsenic caused the world s worst mass poisoning macmillan science two zero zero five external links a small dose of toxicology case studies in environmental medicine arsenic toxicity national pollutant inventory arsenic webelements com arsenic origen net cca wood and arsenic toxicological effects of arsenic contaminant focus arsenic by the epa environmental health criteria for arsenic and arsenic compounds two zero zero one by the who a summary of the above report by greenfacts evaluation of the carcinogenicity of arsenic and arsenic compounds by the iarc metalloids pnictogens toxicology chemica |
l elements antimony is a chemical element in the periodic table that has the symbol sb l stibium and atomic number five one a metalloid antimony has four allotropic forms the stable form of antimony is a blue white metal yellow and black antimony are unstable non metals antimony is used in flame proofing paints ceramics enamels a wide variety of alloys electronics and rubber notable characteristics antimony in its elemental form is a silvery white brittle fusible crystalline solid that exhibits poor electrical and heat conductivity properties and vaporizes at low temperatures a metalloid antimony resembles a metal in its appearance and physical properties but does not chemically react as a metal it is also attacked by oxidizing acids and halogens antimony and some of its alloys expand on cooling estimates of the abundance of antimony in the earth s crust range from zero two to zero five ppm antimony is geochemically categorized as a chalcophile occurring with sulfur and the heavy metals lead copper and silver |
applications antimony is increasingly being used in the semiconductor industry in the production of diodes infrared detectors and hall effect devices as an alloy this semi metal greatly increases lead s hardness and mechanical strength the most important use of antimony metal is as a hardener in lead for storage batteries other uses batteries antifriction alloys type metal small arms and tracer bullets cable sheathing matches medicines plumbing lead free solder contains five sb main and big end bearings in internal combustion engines as alloy used in the past to treat schistosomiasis nowadays praziquantel is universally used antimony compounds in the form of oxides sulfides sodium antimonate and antimony trichloride are used in the making of flame proofing compounds ceramic enamels glass paints and pottery antimony trioxide is the most important of the antimony compounds and is primarily used in flame retardant formulations these flame retardant applications include such markets as children s clothing toys a |
ircraft and automobile seat covers also antimony sulfide is one of the ingredients of a modern match history antimony was recognized in antiquity three zero zero zero bc or earlier in various compounds and it was prized for its fine casting qualities it was first reported scientifically by tholden in one four five zero and was known to be a metal by the beginning of the one seven th century the origin of the name antimony is not clear the term may come from the greek words anti and monos which approximately means opposed to solitude as it was thought never to exist in its pure form or from the pharaonic expression antos amun which could be translated as bloom of the god amun alchemical symbol for antimony the natural sulfide of antimony stibnite was known and used in biblical times as medicine and as a cosmetic stibnite is still used in some developing countries as medicine antimony has been used for the treatment of schistosomiasis antimony attaches itself to sulfur atoms in certain enzymes which are used bo |
th by the parasite and human host small doses can kill the parasite without causing damage to the patient antimony and its compounds are used in several veterinary preparations like anthiomaline or lithium antimony thiomalate which is used as a skin conditioner in ruminants antimony has a nourishing or conditioning effect on keratinized tissues at least in animals tartar emetic is another antimony preparation which is used as an anti schistosomal drug the relationship between antimony s modern name and its symbol is complex the coptic name for the cosmetic powder antimony sulfide was borrowed by the greeks which was in turn borrowed by latin resulting in stibium the chemical pioneer j ns jakob berzelius used an abbreviation of this name for antimony in his writings and his usage became the standard symbol treatments chiefly involving antimony have been called antimonials sources native massive antimony with oxidation products even though this element is not abundant it is found in over one zero zero mineral s |
pecies antimony is sometimes found native but more frequently it is found in the sulfide stibnite sb two s three which is the predominant ore mineral commercial forms of antimony are generally ingots broken pieces granules and cast cake other forms are powder shot and single crystals chiffres de two zero zero three m tal contenue dans les minerais et concentr s source l tat du monde two zero zero five precautions antimony and many of its compounds are toxic clinically antimony poisoning is very similar to arsenic poisoning in small doses antimony causes headache dizziness and depression such small doses have in the past been reported in some acidic fruit drinks the acidic nature of the drink is sufficient to dissolve small amounts of antimony oxide contained in the packaging of the drink modern manufacturing methods prevent this occurrence larger doses cause violent and frequent vomiting and will lead to death in few days very large doses will cause violent vomiting causing the poison to be expelled from the |
body before any harm is done compounds antimony pentafluoride sbf five antimony trioxide sb two o three stibine antimony trihydride sbh three indium antimonide insb see also references los alamos national laboratory antimony public health statement for antimony see also antimonial external links national pollutant inventory antimony and compounds webelements com antimony elementymology elements multidict antimony by peter van der krogt world mine production of antimony by country chemical elements metalloids pnictogens actinium is a chemical element in the periodic table that has the symbol ac and atomic number eight nine notable characteristics actinium is a silvery radioactive metallic element due to its intense radioactivity actinium glows in the dark with an eerie blue light it is found only in traces in uranium ores as two two seven ac an and emitter with a half life of two one seven seven three years one ton of uranium ore contains about a tenth of a gram of actinium applications it is about one five ze |
ro times as radioactive as radium making it valuable as a neutron source otherwise it has no significant industrial applications actinium two two five is used in medicine to produce bi two one three in a reusable generator or can be used alone as an agent for radio immunotherapy history actinium was discovered in one eight nine nine by andr louis debierne a french chemist who separated it from pitchblende friedrich otto giesel independently discovered actinium in one nine zero two the chemical behavior of actinium is similar to that of the rare earth lanthanum the word actinium comes from the greek aktis aktinos meaning beam or ray occurrence actinium is found in trace amounts in uranium ore but more commonly is made in milligram amounts by the neutron irradiation of two two six ra in a nuclear reactor actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about one one zero zero to one three zero zero c isotopes naturally occurring actinium is composed of one radioactive |
isotope two two seven ac three six radioisotopes have been characterized with the most stable being two two seven ac with a half life of two one seven seven two y two two five ac with a half life of one zero zero days and two two six ac with a half life of two nine three seven h all of the remaining radioactive isotopes have half lifes that are less than one zero hours and the majority of these have half lifes that are less than one minute the shortest lived isotope of actinium is two one seven ac which decays through alpha decay and electron capture it has a half life of six nine ns actinium also has two meta states purified actinium two two seven comes into equilibrium with its decay products at the end of one eight five days and then decays according to its two one seven seven three year half life the isotopes of actinium range in atomic weight from two zero six amu two zero six actinium to two three six amu two three six ac precautions actinium two two seven is extremely radioactive and in terms of its p |
otential for radiation induced health effects actinium two two seven is about as dangerous as plutonium ingesting even small amounts of actinium two two seven would present a serious health hazard references los alamos national laboratory actinium external links webelements com actinium chemical elements actinides americium is a synthetic element in the periodic table that has the symbol am and atomic number nine five a radioactive metallic element americium is an actinide that was obtained by bombarding plutonium with neutrons and was the fourth transuranic element to be discovered it was named for the americas by analogy with europium notable characteristics freshly prepared americium metal has a white and silvery luster at room temperatures it slowly tarnishes in dry air it is more silvery than plutonium or neptunium and apparently more malleable than neptunium or uranium alpha emission from am two four one is approximately three times radium gram quantities of am two four one emit intense gamma rays which |
creates a serious exposure problem for anyone handling the element applications this element can be produced in kilogram amounts and has some uses mostly am two four one since it is easier to produce relatively pure samples of this isotope americium has found its way into the household where one type of smoke detector contains a tiny amount of am two four one as a source of ionizing radiation am two four one has been used as a portable gamma ray source for use in radiography the element has also been employed to gauge glass thickness to help create flat glass am two four two is a neutron emitter and has found uses in neutron radiography however this isotope is extremely expensive to produce in usable quantities history americium was first synthesized by glenn t seaborg leon o morgan ralph a james and albert ghiorso in late one nine four four at the wartime metallurgical laboratory at the university of chicago now known as argonne national laboratory the team created the isotope am two four one by subjecting |
plutonium two three nine to successive neutron capture reactions in a nuclear reactor this created pu two four zero and then pu two four one which in turn decayed into am two four one via beta decay seaborg was granted patent three one five six five two three for element nine five and method of producing said element the discovery of americium and curium was first announced informally on a children s quiz show in one nine four five isotopes one eight radioisotopes of americium have been characterized with the most stable being am two four three with a half life of seven three seven zero years and am two four one with a half life of four three two two years all of the remaining radioactive isotopes have half lives that are less than five one hours and the majority of these have half lives that are less than one zero zero minutes this element also has eight meta states with the most stable being am two four two m t one four one years the isotopes of americium range in atomic weight from two three one zero four |
six amu am two three one to two four nine zero seven eight amu am two four nine chemistry in aqueous systems the most common oxidation state is three it is very much harder to oxidise am iii to am iv than it is to do the same oxidation for pu iii currently the solvent extraction chemistry of americium is important as in several areas of the world scientists are working on reducing the medium term radiotoxicity of the waste from the reprocessing of used nuclear fuel see liquid liquid extraction for some examples of the solvent extraction of americium americium like other actinides readily forms a dioxide americyl core amo two in the environment this americyl core readily complexes with carbonate as well as other oxygen moeities oh no two no three and so four two to form charged complexes which tend to be readily mobile with low affinities to soil amo two oh one amo two oh two two amo two co three one one amo two co three two one amo two co three three three references los alamos national laboratory americium g |
uide to the elements revised edition albert stwertka oxford university press one nine nine eight isbn zero one nine five zero eight zero eight three one it s elemental americium external links webelements com americium also used as a reference chemical elements actinides americium compounds astatine is a chemical element in the periodic table that has the symbol at and atomic number eight five this radioactive element occurs naturally from uranium and thorium decay and is the heaviest of the halogens notable characteristics this highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens especially iodine it would probably accumulate in the thyroid gland like iodine astatine is thought to be more metallic than iodine researchers at the brookhaven national laboratory have performed experiments that have identified and measured elementary reactions that involve astatine with the possible exception of francium astatine is the rarest naturally occurring elemen |
t with the total amount in earth s crust estimated to be less than one oz two eight g at any one time this amounts to less than one teaspoon of the element the guinness book of records however has dubbed the element the rarest on earth stating only around zero nine oz two five g of the element astatine at occurs naturally in the earth s crust history astatine greek astatos meaning unstable was first synthesized in one nine four zero by dale r corson k r mackenzie and emilio segr of the university of california berkeley by barraging bismuth with alpha particles an earlier name for the element was alabamine ab occurrence astatine is produced by bombarding bismuth with energetic alpha particles to obtain relatively long lived at two zero nine at two one one which can then be distilled from the target by heating in the presence of air isotopes astatine has four one known isotopes all of which are radioactive the longest lived isotope is two one zero at which has a half life of eight one hours the shortest lived i |
sotope is two one three at which has a half life of one two five nanoseconds references los alamos national laboratory astatine external links webelements com astatine chemical elements halogens bgcolor gray properties in chemistry and physics an atom greek meaning indivisible is the smallest possible particle of a chemical element that retains its chemical properties the word atom may also refer to the smallest possible indivisible fundamental particle this definition must not be confused with that of chemical atoms since chemical atoms hereafter atoms are composed of smaller subatomic particles most atoms are composed of three types of subatomic particles which govern their external properties electrons which have a negative charge and are the least massive of the three protons which have a positive charge and are about one eight three six times more massive than electrons and neutrons which have no charge and are about one eight three eight times more massive than electrons protons and neutrons are both nu |
cleons and make up the dense massive atomic nucleus the electrons form the much larger electron cloud surrounding the nucleus atoms differ in the number of each of the subatomic particles they contain the number of protons in an atom called the atomic number determines the element of the atom within a single element the number of neutrons may also vary determining the isotope of that element atoms are electrically neutral if they have an equal number of protons and electrons electrons that are furthest from the nucleus may be transferred to other nearby atoms or even shared between atoms atoms which have either a deficit or a surplus of electrons are called ions the number of protons and neutrons in the atomic nucleus may also change via nuclear fusion nuclear fission or radioactive decay atoms are the fundamental building blocks of chemistry and are conserved in chemical reactions atoms are able to bond into molecules and other types of chemical compounds molecules are made up of multiple atoms for example a |
molecule of water is a combination of two hydrogen atoms and one oxygen atom properties of the atom subatomic particles see main article subatomic particles although the name atom was applied at a time when atoms were thought to be indivisible it is now known that the atom can be broken down into a number of smaller components the first of these to be discovered was the negatively charged electron which is easily ejected from atoms during ionization the electrons orbit a small dense body containing all of the positive charge in the atom called the atomic nucleus this nucleus is itself made up of nucleons positively charged protons and chargeless neutrons before one nine six one the subatomic particles were thought to consist of only protons neutrons and electrons however protons and neutrons themselves are now known to consist of still smaller particles called quarks in addition the electron is known to have a nearly massless neutral partner called a neutrino together the electron and neutrino are both lepto |
ns ordinary atoms are composed only of quarks and leptons of the first generation the proton is composed of two up quarks and one down quark whereas the neutron is composed of one up quark and two down quarks although they do not occur in ordinary matter two other heavier generations of quarks and leptons may be generated in high energy collisions the subatomic force carrying particles called gauge bosons are also important to atoms electrons are bound to the nucleus by photons carrying the electromagnetic force protons and neutrons are bound together in the nucleus by gluons carrying the strong nuclear force electron configuration see main article electron configuration the chemical behavior of atoms is due to interactions between electrons electrons of an atom remain within certain predictable electron configurations these configurations are determined by the quantum mechanics of electrons in the electric potential of the atom the principal quantum number determines particular electron shells with distinct |
energy levels generally the higher the energy level of a shell the further away it is from the nucleus the electrons in the outermost shell called the valence electrons have the greatest influence on chemical behavior core electrons those not in the outer shell play a role but it is usually in terms of a secondary effect due to screening of the positive charge in the atomic nucleus the atomic orbital wavefunctions of a hydrogen atom the principal quantum number is at the right of each row and the azimuthal quantum number is denoted by letter at top of each column an electron shell can hold up to two n two electrons where n is the principal quantum number of the shell the occupied shell of greatest n is the valence shell even if it only has one electron in the most stable ground state an atom s electrons will fill up its shells in order of increasing energy under some circumstances an electron may be excited to a higher energy level that is it absorbs energy from an external source and leaps to a higher shell |
leaving a space in a lower shell an excited atom s electrons will spontaneously fall into lower levels emitting excess energy as a photons until it returns to the ground state in addition to its principal quantum number n an electron is distinguished by three other quantum numbers the azimuthal quantum number l describing the orbital angular momentum of the electron the magnetic quantum number m describing the direction of the angular momentum vector and the spin quantum number s describing the direction of the electron s intrinsic angular momentum electrons with varying l and m have distinctive shapes denoted by spectroscopic notation in the illustration the letters s p d and f corresponding to l zero one two three describe the shape of the atomic orbital in most atoms orbitals of differing l are not exactly degenerate but separated into a fine structure orbitals of differing m are degenerate but may be separated by applying a magnetic field creating the zeeman effect electrons with differing s have very sli |
ght energy differences called hyperfine splitting nucleon properties the constituent protons and neutrons of the atomic nucleus are collectively called nucleons the nucleons are held together in the nucleus by the strong nuclear force nuclei can undergo transformations that affect the number of protons and neutrons they contain a process called radioactive decay when nuclei transformations take place spontaneously this process is called radioactivity radioactive transformations proceed by a wide variety of modes but the most common are alpha decay emission of a helium nucleus and beta decay emission of an electron decays involving electrons or positrons are due to the weak nuclear interaction in addition like the electrons of the atom the nucleons of nuclei may be pushed into excited states of higher energy however these transitions typically require thousands of times more energy than electron excitations when an excited nucleus emits a photon to return to the ground state the photon has very high energy and |
is called a gamma ray nuclear transformations also take place in nuclear reactions in nuclear fusion two light nuclei come together and merge into a single heavier nucleus in nuclear fission a single large nucleus is divided into two or more smaller nuclei atom size and speed atoms are much smaller than the wavelengths of light that human vision can detect so atoms cannot be seen in any kind of optical microscope however there are ways of detecting the positions of atoms on the surface of a solid or a thin film so as to obtain images these include electron microscopes such as in scanning tunneling microscopy stm atomic force microscopy afm nuclear magnetic resonance nmr and x ray microscopy since the electron cloud does not have a sharp cutoff the size of an atom is not easily defined for atoms that can form solid crystal lattices the distance between the centers of adjacent atoms can be easily determined by x ray diffraction giving an estimate of the atoms size for any atom one might use the radius at which |
the electrons of the valence shell are most likely to be found as an example the size of a hydrogen atom is estimated to be approximately one zero five eight six one zero m twice the bohr radius compare this to the size of the proton the only particle in the nucleus of the hydrogen atom which is approximately one zero m so the ratio of the size of the hydrogen atom to its nucleus is about one zero zero zero zero zero one if an atom were the size of a stadium the nucleus would be the size of a marble nearly all the mass of an atom is in its nucleus yet almost all the space in an atom is filled by its electrons atoms of different elements do vary in size but the sizes do not scale linearly with the mass of the atom their sizes are roughly the same to within a factor of two the reason for this is that heavy elements have large positive charge on their nuclei which strongly attract the electrons to the center of the atom this contracts the size of the electron shells so that more electrons fit in the only a slig |
htly greater volume the temperature of a collection of atoms is a measure of the average energy of motion of those atoms at zero kelvins absolute zero atoms would have no motion as the temperature of the system is increased the kinetic energy of the particles in the system is increased and their speed of motion increases at room temperature atoms making up gases in the air move at a speed of five zero zero m s about one one zero zero mph or one eight zero zero km h elements isotopes and ions atoms are generally classified by their atomic number z which corresponds to the number of protons in the atom the atomic number determines which chemical element the atom is for example carbon atoms are atoms containing six protons all atoms with the same atomic number share a wide variety of physical properties and exhibit the same chemical properties the elements may be sorted according to the periodic table in order of increasing atomic number the atomic mass a atomic mass number or nucleon number of an element is the |
total number of protons and neutrons in an atom of that element so called because each proton and neutron has a mass of about one amu the number of neutrons a z in an atom has no effect on which element it is each element can have numerous kinds of atoms with the same number of protons and electrons but varying numbers of neutrons each has the same atomic number but a different mass number these are called the isotopes of an element when writing the name of an isotope the element name is followed by the mass number for example carbon one four contains six protons and eight neutrons in each atom for a total mass number of one four the atomic mass listed for each element in the periodic table is an average of the isotope masses found in nature weighted by their abundance the simplest atom is the hydrogen isotope protium which has atomic number one and atomic mass number one it consists of one proton and one electron the hydrogen isotope which also contains one neutron so is called deuterium or hydrogen two the |
hydrogen isotope with two neutrons is called tritium or hydrogen three tritium is an unstable isotope which decays through a process called radioactivity almost all isotopes of each element are radioactive only a few are stable the elements with atomic number eight four polonium and heavier have no stable isotopes and are all radioactive virtually all elements heavier than hydrogen and helium were created through stellar nucleosynthesis and supernova nucleosynthesis most of the elements lighter than uranium z nine two have stable enough isotopes to occur naturally on earth with the notable exception of technetium z four three several elements that do not occur on earth have been found to be present in stars elements not normally found in nature have been artificially created by nuclear bombardment as of two zero zero six elements have been created through atomic number one one six given the temporary name ununhexium these ultra heavy elements are generally highly unstable and decay quickly atoms that have ei |
ther lost or gained electrons are called atomic ions with either positive or negative charge respectively valence and bonding see main article valence electrons and chemical bond the number of electrons in an atom s outermost shell the valence shell governs its bonding behavior therefore elements with the same number of valence electrons are grouped together in the columns of the periodic table of the elements alkali metals contain one electron on their outer shell alkaline earth metals two electrons halogens seven electrons and various others every atom is most stable with a full valence shell this means that atoms with full valence shells the noble gases are very unreactive conversely atoms with few electrons in their valence shell are more reactive it is alkali metals are therefore very reactive with caesium rubidium and francium being the most reactive of all metals also atoms that need only few electrons such as the halogens to fill their valence shells are reactive fluorine is the most reactive of all e |
lements atoms may fill their valence shells by chemical bonding this can be achieved one of two ways an atom can either share electrons with other atoms a covalent bond or it can remove electrons from or donate electrons to other atoms an ionic bond the formation of a bond causes a strong attraction between two atoms creating molecules or ionic compounds many other types of bonds exist including polar covalent bonds coordinate covalent bonds metallic bonds hydrogen bonds and van der waals bonds atomic spectrum see main article atomic spectroscopy since each element in the periodic table consists of an atom in a unique configuration with different numbers of protons and electrons each element can also be uniquely described by the energies of its atomic orbitals and the number of electrons within them normally an atom is found in its lowest energy ground state states with higher energy are called excited states an electron may move from a lower energy orbital to a higher energy orbital by absorbing a photon wit |
h energy equal to the difference between the energies of the two levels an electron in a higher energy orbital may drop to a lower energy orbital by emitting a photon since each element has a unique set of energy levels each creates its own light pattern unique to itself its own spectral signature if a set of atoms is heated such as in an arc lamp their electrons will move into excited states when these atoms fall back toward the ground state they will produce an emission spectrum if a set of atoms is illuminated by a continuous spectrum it will only absorb specific wavelengths energies of photon that correspond to the differences in its energy levels the resulting pattern of gaps is called the absorption spectrum in spectroscopic analysis scientists can use a spectrometer to study the atoms in stars and other distant objects due to the distinctive spectral lines that each element produces they are able to tell the chemical composition of distant planets stars and nebulae not all parts of the atomic spectrum |
are in visible light part of the electromagnetic spectrum for example the hyperfine transitions including the important two one cm line produce low energy radio waves when electrons deep inside large atoms are knocked out for example by beta radiation replacement atoms fall deep into the electric potential of the nucleus producing high energy x rays atoms and antimatter see main article antimatter antimatter can also form atoms composed of positrons antiprotons and antineutrons since antimatter is very difficult to produce and store only a small amount antihydrogen has ever existed on earth this was produced at cern in the athena and atrap experiments using the antiproton decelerator atoms and the big bang in models of the big bang big bang nucleosynthesis predicts that within one to three minutes of the big bang almost all atomic material in the universe was created during this process nuclei of hydrogen and helium formed abundantly but almost no elements heavier than lithium hydrogen makes up approximately |
seven five of the atoms in the universe helium makes up two four and all other elements make up just one however although nuclei fully ionized atoms were created neutral atoms themselves could not form in the intense heat big bang chronology of the atom continues to approximately three seven nine zero zero zero years after the big bang when the cosmic temperature had dropped to just three zero zero zero k it was then cool enough to allow the nuclei to capture electrons this process is called recombination during which the first neutral atoms took form once atoms become neutral they only absorb photons of a discrete absorption spectrum this allows most of the photons in the universe to travel unimpeded for billions of years these photons are still detectable today in the cosmic microwave background after big bang nucleosynthesis no heavier elements could be created until the formation of the first stars these stars fused heavier elements through stellar nucleosynthesis during their lives and through supernova |
nucleosynthesis as they died the seeding of the interstellar medium by heavy elements eventually allowed the formation of terrestrial planets like the earth history of atomic theory early atomism from the six th century bc hindu buddhist and jaina philosophers in ancient india developed the earliest atomic theories the first philosopher who formulated ideas about the atom in a systematic manner was kanada who lived in the six th century bc another indian philosopher pakudha katyayana who also lived in the six th century bc and was a contemporary of gautama buddha had also propounded ideas about the atomic constitution of the material world indian atomists believed that an atom could be one of upto six elements with each element having upto two four properties they developed detailed theories of how atoms could combine react vibrate move and perform other actions and had particularly elaborate theories of how atoms combine which explains how atoms first combine in pairs and then group into trios of pairs which |
are the smallest visible units of matter this parallels with the structure of modern atomic theory in which pairs or triplets of supposedly fundamental quarks combine to create most typical forms of matter they had also suggested the possibility of splitting an atom which as we know today is the source of atomic energy see indian atomism for more details democritus and leucippus greek philosophers in the five th century bc presented a theory of atoms see atomism for more details the greeks believed that atoms were all made of the same material but had different shapes and sizes which determined the physical properties of the material for instance the atoms of a liquid were thought to be smooth allowing them to slide over each other none of these ideas however were founded in scientific experimentation during the middle ages the islamic golden age islamic atomists develop atomic theories that represent a synthesis of both greek and indian atomism see islamic atomism for more details older greek and indian ide |
as were further developed by islamic atomists along with new islamic ideas such as the possibility of there being particles smaller than an atom as islamic influence began spreading through europe the ideas of islamic atomism along with the older ideas of greek and indian atomism spread throughout europe by the end of the middle ages where modern atomic theories began taking shape birth of modern atomic theory in one eight zero eight john dalton proposed that an element is composed of atoms of a single unique type and that although their shape and structure was immutable atoms of different elements could combine to form more complex structures chemical compounds he deduced this after the experimental discovery of the law of multiple proportions that is if two elements form more than one compound between them then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers the experiment in question involved combining nitrous oxide n |
o with oxygen o two in one combination these gases formed dinitrogen trioxide n two o three but when he repeated the combination with double the amount of oxygen a ratio of one two they instead formed nitrogen dioxide no two four no o two two n two o three four no two o two four no two atomic theory conflicted with the theory of infinite divisibility which states that matter can always be divided into smaller parts in one eight two seven biologist robert brown observed that pollen grains floating in water constantly jiggled about for no apparent reason in one nine zero five albert einstein theorised that this brownian motion was caused by the water molecules continuously knocking the grains about and developed a mathematical theory around it this theory was validated experimentally in one nine one one by french physicist jean perrin discovery of subatomic particles for much of this time atoms were thought to be the smallest possible division of matter however in one eight nine seven j j thomson published his |
work proving that cathode rays are made of negatively charged particles electrons since cathode rays are emitted from matter this proved that atoms are made up of subatomic particles and are therefore divisible and not the indivisible atomos postulated by democritus physicists later invented a new term for such indivisible units elementary particles since the word atom had come into its common modern use study of atomic structure at first it was believed that the electrons were distributed more or less uniformly in a sea of positive charge the plum pudding model however an experiment conducted in one nine zero nine by colleagues of ernest rutherford demonstrated that atoms have a most of their mass and positive charge concentrated in a nucleus in the gold foil experiment alpha particles emitted by polonium were shot through a sheet of gold rutherford observed that most of the particles passed straight through the sheet with little deflection striking a fluorescent screen on the other side about one in eight z |
ero zero zero of the alpha particles however were heavily deflected by more than nine zero degrees this led to the planetary model of the atom in which pointlike electrons orbited in the space around a massive compact nucleus like planets orbiting the sun the nucleus was later discovered to contain protons and further experimentation by rutherford found that the nuclear mass of most atoms surpassed that of the protons it possessed this led him to postulate the existence of neutrons whose existence would be proven in one nine three two by james chadwick the planetary model of the atom still had shortcomings firstly a moving electric charge emits electromagnetic waves according to classical electromagnetism an orbiting charge would steadily lose energy and spiral towards the nucleus colliding with it in a tiny fraction of a second secondly the model did not explain why excited atoms emit light only in certain discrete spectra quantum theory revolutionized physics at the beginning of the two zero th century when |
max planck and albert einstein postulated that light energy is emitted or absorbed in fixed amounts known as quanta in one nine one three niels bohr used this idea in his bohr model of the atom in which the electrons could only orbit the nucleus in particular circular orbits with fixed angular momentum and energy they were not allowed to spiral into the nucleus because they could not lose energy in a continuous manner they could only make quantum leaps between fixed energy levels bohr s model was extended by arnold sommerfeld in one nine one six to include elliptical orbits using a quantization of generalized momentum the ad hoc bohr sommerfeld model was extremely difficult to use but it made impressive predictions in agreement with certain spectral properties however the model was unable to explain multielectron atoms predict transition rates or describe fine and hyperfine structure in one nine two five erwin schr dinger developed a full theory of quantum mechanics described by the schr dinger equation toge |
ther with wolfgang pauli s exclusion principle this allowed study of atoms with great precision when digital computers became available even today these theories are used in the hartree fock quantum chemical method to determine the energy levels of atoms further refinements of quantum theory such as the dirac equation and quantum field theory made smaller impacts on the theory of atoms another model of historical interest proposed by gilbert n lewis in one nine one six had cubical atoms with electrons statically held at the corners the cubes could share edges or faces to form chemical bonds this model was created to account for chemical phenomena such as bonding rather than physical phenomena such as atomic spectra see also atomism basic quantum mechanics chemical bond exotic atom infinite divisibility list of particles radioactive isotope superatom super heavy atom transuranium element references kenneth s krane introductory nuclear physics one nine eight seven external links how atoms work wikibooks fhsst p |
hysics atom the atom wikibooks atomic structure atoms modern arable agriculture typically uses large fields like this one in dorset england in geography arable land from latin arare to plough is a form of agricultural land use meaning land that can be and is used for growing crops david ricardo incorporated the idea of arable land into economic theory of the earth s five seven million square miles one four eight zero zero zero zero zero zero km of land more than one two million square miles three one zero zero zero zero zero zero km are arable most of the arable land on earth is around the largest rivers on earth some examples are the nile river the tigris and euphrates rivers the yellow river the amazon river the ganges and the rhine river these rivers flood regularly overspilling their banks when the flood is over the rivers recede leaving behind rich silt this silt is excellent fertilizer for crops even if the land is overfarmed and all the nutrients are depleted from the soil the land renews its fertility |
when the next flood comes rivers and streams can make desert land arable unarable land on unarable land farming is nearly impossible unless more advanced methods of agriculture are used unarable land usually has no source of fresh water and is often too hot desert too cold arctic too rocky too mountainous too salty too rainy too snowy or too cloudy clouds block the sunlight plants need for photosynthesis making sunlight into food the plants starve without light starvation and nomadism often exist on unarable land unarable land is sometimes called wastes badlands worthless or no man s land sometimes unarable land can be turned into arable land new arable land makes more food and can prevent starvation saving lives this also makes the country more self sufficient and politically independent because the country doesn t have to buy food from other countries making unarable land arable often involves digging new irrigation canals and new wells aquaducts desalination plants planting trees for shade in the desert h |
ydroponics fertilizer nitrogen fertilizer pesticides reverse osmosis water processors mylar insulation or other insulation against heat and cold digging ditches and hills for protection against the wind and greenhouses with internal light and heat for protection against the cold outside and to provide light in cloudy areas some examples of infertile unarable land being turned into fertile arable land are aran island this island off the west coast of ireland not to be confused with the isle of arran in scotland s firth of clyde was unarable because it was too rocky the people covered the island with a shallow layer of seaweed and sand from the ocean this made it arable today they grow crops there israel israel was mostly unarable desert until desalination plants were built on the coast the plants turn salt water into fresh water for farming drinking and washing they created their own large fresh water source some examples of fertile arable land being turned into infertile unarable land are droughts like the du |
st bowl of the great depression in the u s turned farmland into desert rainforest deforestation the fertile tropical forests turn into infertile desert land romans destruction of carthage at the end of the punic wars the victorious romans sowed the earth with salt to symbolize total victory the roman symbol meant that carthage would never grow back their civilization ended crops won t generally grow in salty soil this is why salt water from the ocean can t be used to water crops each year more arable land is lost to desertification and erosion from human industrial activities irrigation of farm land also increases the sodium calcium and magnesium in the soil this process steadily concentrates salt in the ground decreasing productivity for crops that are not salt tolerant urban sprawl in the united states about two two million acres eight nine zero zero km of land was added to urban areas between one nine nine two and two zero zero two much of it farm land now paved see also list of environment topics external |
links surface area of the earth conserving land population and sustainable food production agriculture horticulture aluminium or aluminum see the spelling section below is the chemical element in the periodic table that has the symbol al and atomic number one three it is a silvery and ductile member of the poor metal group of chemical elements aluminium is found primarily as the ore bauxite and is remarkable for its resistance to corrosion due to the phenomenon of passivation and its light weight aluminium is used in many industries to make millions of different products and is very important to the world economy structural components made from aluminium and its alloys are vital to the aerospace industry and very important in other areas of transportation and building in which light weight durability and strength are needed properties a piece of aluminium metal about one five centimetres long aluminium is a soft and lightweight metal with a dull silvery appearance due to a thin layer of oxidation that forms |
quickly when it is exposed to air aluminium is nontoxic as the metal non magnetic and non sparking pure aluminium has a tensile strength of about four nine megapascals mpa and four zero zero mpa if it is formed into an alloy aluminium is about one third as dense as steel or copper is malleable ductile and easily machined and cast and has excellent corrosion resistance and durability due to the protective oxide layer aluminium mirror finish has the highest reflectance of any metal in the two zero zero four zero zero nm uv and the three zero zero zero one zero zero zero zero nm far ir regions while in the four zero zero seven zero zero nm visible range it is slightly outdone by silver and in the seven zero zero three zero zero zero near ir by silver gold and copper it is the second most malleable metal after gold and the sixth most ductile aluminium is a good heat conductor which is why it is used to make saucepans bohr diagram applications whether measured in terms of quantity or value the use of aluminium exc |
eeds that of any other metal except iron and it is important in virtually all segments of the world economy pure aluminium has a low tensile strength but readily forms alloys with many elements such as copper zinc magnesium manganese and silicon e g duralumin today almost all materials that claim to be aluminium are actually an alloy thereof pure aluminium is encountered only when corrosion resistance is more important than strength or hardness conversely the term alloy in general use today usually means aluminium alloy when combined with thermo mechanical processing aluminium alloys display a marked improvement in mechanical properties aluminium alloys form vital components of aircraft and rockets as a result of their high strength to weight ratio when aluminium is evaporated in a vacuum it forms a coating that reflects both visible light and infrared these coatings form a thin layer of protective aluminium oxide that does not deteriorate as silver coatings do in particular nearly all modern mirrors are made |
using a thin reflective coating of aluminium on the back surface of a sheet of float glass telescope mirrors are also coated with a thin layer of aluminium but are front coated to avoid internal reflections even though this makes the surface more susceptible to damage an aluminium can used for the soft drink diet coke some of the many uses for aluminium are in transportation automobiles airplanes trucks railroad cars marine vessels bicycles etc packaging cans foil etc water treatment construction windows doors siding building wire etc consumer durable goods appliances cooking utensils etc electrical transmission lines aluminium components and wires are less dense than those made of copper and are lower in price but also present higher electrical resistance many localities prohibit the use of aluminum in residential wiring practices because of its higher resistance and thermal expansion value machinery mkm steel and alnico magnets although non magnetic itself super purity aluminium spa nine nine nine eight ze |
ro to nine nine nine nine nine al used in electronics and cds powdered aluminium a commonly used silvering agent in paint aluminium flakes may also be included in undercoat paints particularly wood primer on drying the flakes overlap to produce a water resistant barrier anodised aluminium is more stable to further oxidation and is used in various fields of construction as well as heat sinking most electronic appliances that require cooling of their internal devices like transistors cpus semiconductors in general have heat sinks that are made of aluminium due to its ease of manufacture and good heat conductivity copper heat sinks are smaller although more expensive and harder to manufacture aluminium oxide alumina is found naturally as corundum rubies and sapphires emery and is used in glass making synthetic ruby and sapphire are used in lasers for the production of coherent light aluminium oxidises very energetically and as a result has found use in solid rocket fuels thermite and other pyrotechnic compositio |
ns aluminium is also a superconductor with a superconducting critical temperature of one two kelvins engineering use aluminium alloys with a wide range of properties are used in engineering structures alloy systems are classified by a number system ansi or by names indicating their main alloying constituents din and iso selecting the right alloy for a given application entails considerations of strength ductility formability weldability and corrosion resistance to name a few a brief historical overview of alloys and manufacturing technologies is given in ref improper use of aluminium can result in problems particularly in contrast to iron or steel which appear better behaved to the intuitive designer mechanic or technician the reduction by two thirds of the weight of an aluminium part compared to a similarly sized iron or steel part seems enormously attractive but it should be noted that it is accompanied by a reduction by two thirds in the stiffness of the part therefore although direct replacement of an iro |
n or steel part with a duplicate made from aluminium may still give acceptable strength to withstand peak loads the increased flexibility will cause three times more deflection in the part where failure is not an issue but excessive flex is undesirable due to requirements for precision of location or efficiency of transmission of power simple replacement of steel tubing with similarly sized aluminium tubing will result in a degree of flex which is undesirable for instance the increased flex under operating loads caused by replacing steel bicycle frame tubing with aluminium tubing of identical dimensions will cause misalignment of the power train as well as absorbing the operating force to increase the rigidity by increasing the thickness of the walls of the tubing increases the weight proportionately so that the advantages of lighter weight are lost as the rigidity is restored aluminium can best be used by redesigning the part to suit its characteristics for instance making a bicycle of aluminium tubing which |
has an oversize diameter rather than thicker walls in this way rigidity can be restored or even enhanced without increasing weight the limit to this process is the increase in susceptibility to what is termed buckling failure where the deviation of the force from any direction other than directly along the axis of the tubing causes folding of the walls of the tubing the latest models of the corvette automobile among others are a good example of redesigning parts to make best use of aluminium s advantages the aluminium chassis members and suspension parts of these cars have large overall dimensions for stiffness but are lightened by reducing cross sectional area and removing unneeded metal as a result they are not only equally or more durable and stiff as the usual steel parts but they possess an airy gracefulness which most people find attractive similarly aluminium bicycle frames can be optimally designed so as to provide rigidity where required yet have flexibility in terms of absorbing the shock of bumps |
from the road and not transmitting them to the rider the strength and durability of aluminium varies widely not only as a result of the components of the specific alloy but also as a result of the particular manufacturing process for this reason it has from time to time gained a bad reputation for instance a high frequency of failure in many early aluminium bicycle frames in the one nine seven zero s resulted in just such a poor reputation with a moment s reflection however the widespread use of aluminium components in the aerospace and automotive high performance industries where huge stresses are undergone with vanishingly small failure rates proves that properly built aluminium bicycle components should not be unusually unreliable and this has subsequently proved to be the case similarly use of aluminium in automotive applications particularly in engine parts which must survive in difficult conditions has benefited from development over time an audi engineer commented about the v one two engine producing o |
ver five zero zero horsepower three seven zero kw of an auto union race car of the one nine three zero s which was recently restored by the audi factory that the aluminium alloy of which the engine was constructed would today be used only for lawn furniture and the like even the aluminium cylinder heads and crankcase of the corvair built as recently as the one nine six zero s earned a reputation for failure and stripping of threads in holes even as large as spark plug holes which is not seen in current aluminium cylinder heads often aluminium s sensitivity to heat must also be considered even a relatively routine workshop procedure involving heating is complicated by the fact that aluminium as opposed to steels will melt without first turning red forming operations where a blow torch is used therefore requires some expertise since no visual signs reveal how close the material is to melting aluminium also will accumulate internal stresses and strains under conditions of overheating while not immediately obviou |
s the tendency of the metal to creep under sustained stresses results in delayed distortions for instance the commonly observed warping or cracking of aluminium automobile cylinder heads after an engine is overheated sometimes as long as years later or the tendency of welded aluminium bicycle frames to gradually twist out of alignment from the stresses accumulated during the welding process for this reason many uses of aluminium in the aerospace industry avoid heat altogether by joining parts using adhesives this was also used for some of the early aluminium bicycle frames in the one nine seven zero s with unfortunate results when the aluminium tubing corroded slightly loosening the bond of the adhesive and leading to failure of the frame stresses from overheating aluminium can be relieved by heat treating the parts in an oven and gradually cooling in effect annealing the stresses this can also result however in the part becoming distorted as a result of these stresses so that such heat treating of welded bic |
ycle frames for instance results in a significant fraction becoming misaligned if the misalignment is not too severe once cooled they can be bent back into alignment with no negative consequences of course if the frame is properly designed for rigidity see above this will require enormous force household wiring because of its high conductivity and relatively low price compared to copper at the time aluminium was introduced for household electrical wiring to a large degree in the united states in the one nine six zero s unfortunately many of the wiring fixtures at the time were not designed to accept aluminium wire more specifically the greater coefficient of thermal expansion of aluminium causes the wire to expand and contract relative to the dissimilar metal screw connection eventually loosening the connection pure aluminium has a tendency to creep under steady sustained pressure to a greater degree as the temperature rises again producing a degree of looseness in an initially tight connection galvanic corro |
sion from the dissimilar metals increases the electrical resistance of the connection in combination these properties caused connections between electrical fixtures and aluminium wiring to overheat which resulted in several fires as a result aluminium household wiring has become unpopular and in many jurisdictions it is not permitted in very small sizes in new construction however aluminium wiring can be safely used with fixtures whose connections are designed to avoid loosening and overheating older fixtures of this type are marked al cu and newer ones are marked co alr otherwise aluminium wiring can be terminated by crimping it to a short pigtail of copper wire which can be treated as any other copper wire a properly done crimp requiring high pressure produced by the proper tool is tight enough not only to eliminate any thermal expansion of the aluminium but also to exclude any atmospheric oxygen and thus prevent corrosion between dissimilar metals new alloys are used for aluminium building wire today in co |
mbination with aluminium terminations connections made with these standard industry products are as safe and reliable as copper connections see also aluminium wire history the ancient greeks and romans used salts of this metal as dyeing mordants and as astringents for dressing wounds and alum is still used as a styptic further joseph needham suggested finds in one nine seven four showed the ancient chinese used aluminium see notes linked above in one seven six one guyton de morveau suggested calling the base alum alumine in one eight zero eight humphry davy identified the existence of a metal base of alum which he named see spelling section friedrich w hler is generally credited with isolating aluminium latin alumen alum in one eight two seven by mixing anhydrous aluminium chloride with potassium however the metal had been produced for the first time two years earlier in an impure form by the danish physicist and chemist hans christian rsted therefore almanacs and chemistry sites often list rsted as the disco |
verer of aluminium still it would further be p berthier who discovered aluminium in bauxite ore and successfully extracted it the frenchman henri saint claire deville improved w hler s method in one eight four six and described his improvements in a book in one eight five nine chief among these being the substitution of sodium for the considerably more expensive potassium the american charles martin hall of oberlin oh applied for a patent four zero zero six five five in one eight eight six for an electrolytic process to extract aluminium using the same technique that was independently being developed by the frenchman paul h roult in europe the invention of the hall h roult process in one eight eight six made extracting aluminium from minerals cheaper and is now the principal method in common use throughout the world the hall heroult process cannot produce super purity aluminium directly upon approval of his patent in one eight eight nine hall with the financial backing of alfred e hunt of pittsburgh pa starte |
d the pittsburgh reduction company renamed to aluminum company of america in one nine zero seven later shortened to alcoa the statue known as eros in piccadilly circus london was made in one eight nine three and is one of the first statues to be cast in aluminium aluminium was selected as the material to be used for the apex of the washington monument at a time when one ounce cost twice the daily wages of a common worker in the project germany became the world leader in aluminium production soon after adolf hitler seized power by one nine four two however new hydroelectric power projects such as the grand coulee dam gave the united states something nazi germany could not hope to compete with namely the capability of producing enough aluminium to manufacture sixty thousand warplanes in four years natural occurrence although aluminium is the most abundant metallic element in earth s crust believed to be seven five to eight one it is very rare in its free form and was once considered a precious metal more valuab |
le than gold napoleon iii of france had a set of aluminium plates reserved for his finest guests others had to make do with gold ones aluminium has been produced in commercial quantities for just over one zero zero years aluminium was when it was first discovered extremely difficult to separate from its ore aluminium is among the most difficult metals on earth to refine despite the fact that it is one of the planet s most common the reason is that aluminium is oxidised very rapidly and that its oxide is an extremely stable compound that unlike rust on iron does not flake off the very reason for which aluminium is used in many applications is why it is so hard to produce recovery of this metal from scrap via recycling has become an important component of the aluminium industry recycling involves simply melting the metal which is far less expensive than creating it from ore refining aluminium requires enormous amounts of electricity recycling it requires only five of the energy to produce it a common practice s |
ince the early one nine zero zero s aluminium recycling is not new it was however a low profile activity until the late one nine six zero s when the exploding popularity of aluminium beverage cans finally placed recycling into the public consciousness other sources for recycled aluminium include automobile parts windows and doors appliances containers and other products aluminium is a reactive metal and it is hard to extract it from its ore aluminium oxide al two o three direct reduction with carbon for example is not economically viable since aluminium oxide has a melting point of about two zero zero zero c therefore it is extracted by electrolysis the aluminium oxide is dissolved in molten cryolite and then reduced to the pure metal by this process the actual operational temperature of the reduction cells is around nine five zero to nine eight zero c cryolite was originally found as a mineral on greenland but has been replaced by a synthetic cryolite cryolite is a mixture of aluminium sodium and calcium flu |
orides na three alf six the aluminium oxide a white powder is obtained by refining bauxite which is red since it contains three zero to four zero iron oxide this is done using the so called bayer process previously the deville process was the predominant refining technology the electrolytic process replaced the w hler process which involved the reduction of anhydrous aluminium chloride with potassium both of the electrodes used in the electrolysis of aluminium oxide are carbon once the ore is in the molten state its ions are free to move around the reaction at the negative cathode is al three three e al here the aluminium ion is being reduced electrons are added the aluminium metal then sinks to the bottom and is tapped off at the positive electrode anode oxygen gas is formed two o two o two four e this carbon anode is then oxidised by the oxygen the anodes in a reduction must therefore be replaced regularly since they are consumed in the process o two c co two contrary to the anodes the cathodes are not cons |
umed during the operation since there is no oxygen present at the cathode the carbon cathode is protected by the liquid aluminium inside the cells cathodes do erode mainly due to electrochemical processes after five to one zero years depending on the current used in the electrolysis a cell has to be reconstructed completely because the cathodes are completely worn aluminium electrolysis with the hall h roult process consumes a lot of energy but alternative processes were always found to be less viable economically and or ecologically the world wide average specific energy consumption is approximately one five zero five kilowatt hours per kilogram of aluminium produced five two to five six mj kg the most modern smelters reach approximately one two eight kw h kg four six one mj kg reduction line current for older technologies are typically one zero zero to two zero zero ka state of the art smelters operate with about three five zero ka trials have been reported with five zero zero ka cells electric power repres |
ents about two zero to four zero of the cost of producing aluminium depending on the location of the aluminium smelter smelters tend to be located where electric power is plentiful and inexpensive such as south africa the south island of new zealand australia china middle east russia iceland and quebec in canada in two zero zero four china was the top world producer of aluminium suriname depends on aluminium exports for seven zero of its export earnings see also isotopes aluminium has nine isotopes whose mass numbers range from two three to three zero only two seven al stable isotope and two six al radioactive isotope t one two seven two one zero five y occur naturally however two seven al has a natural abundance of one zero zero two six al is produced from argon in the atmosphere by spallation caused by cosmic ray protons aluminium isotopes have found practical application in dating marine sediments manganese nodules glacial ice quartz in rock exposures and meteorites the ratio of two six al to one zero be h |
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