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L_0920 | hydrogen and alkali metals | T_4516 | Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another. Q: Why do you think hydrogen gas usually exists as diatomic molecules? A: Each hydrogen atom has just one electron. When two hydrogen atoms bond together, they share a pair of electrons. The shared electrons fill their only energy level, giving them the most stable arrangement of electrons. Potassium is a soft, silvery metal that ignites explosively in water. It easily loses its one valence electron to form positive potassium ions (K+ ), which are needed by all living cells. Potassium is so impor- tant for plants that it is found in almost all fertilizers, like the one shown here. Potassium is abundant in Earths crust in minerals such as feldspar. Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, as you can see in the atomic model on the right, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time. Q: Francium decays too quickly to form compounds with other elements. Which elements to you think it would bond with if it could? A: With one valence electron, francium would bond with a halogen element in group 17, which has seven valence electrons and needs one more to fill its outer energy level. Elements in group 17 include fluorine and chlorine. | text | null |
L_0921 | hydrogen bonding | T_4517 | Polar compounds, such as water, are compounds that have a partial negative charge on one side of each molecule and a partial positive charge on the other side. All polar compounds contain polar bonds (although not all compounds that contain polar bonds are polar.) In a polar bond, two atoms share electrons unequally. One atom attracts the shared electrons more strongly, so it has a partial negative charge. The other atom attracts the shared electrons less strongly, so it is has a partial positive charge. In a water molecule, the oxygen atom attracts the shared electrons more strongly than the hydrogen atoms do. This explains why the oxygen side of the water molecule has a partial negative charge and the hydrogen side of the molecule has a partial positive charge. Q: If a molecule is polar, how might this affect its interactions with nearby molecules of the same compound? A: Opposite charges on different molecules of the same compound might cause the molecules to be attracted to each other. | text | null |
L_0921 | hydrogen bonding | T_4518 | Because of waters polarity, individual water molecules are attracted to one another. You can see this in the Figure of a nearby water molecule. This force of attraction is called a hydrogen bond. Hydrogen bonds are intermolecular (between-molecule) bonds, rather than intramolecular (within-molecule) bonds. They occur not only in water but in other polar molecules in which positive hydrogen atoms are attracted to negative atoms in nearby molecules. Hydrogen bonds are relatively weak as chemical bonds go. For example, they are much weaker than the bonds holding atoms together within molecules of covalent compounds. Click image to the left or use the URL below. URL: | text | null |
L_0921 | hydrogen bonding | T_4519 | Changes of state from solid to liquid and from liquid to gas occur when matter gains energy. The energy allows individual molecules to separate and move apart from one another. It takes more energy to bring about these changes of state for polar molecules. Although hydrogen bonds are weak, they add to the energy needed for molecules to move apart from one another, so it takes higher temperatures for these changes of state to occur in polar compounds. This explains why polar compounds have relatively high melting and boiling points. The Table 1.1 compares melting and boiling points for some polar and nonpolar covalent compounds. Name of Compound (Chemical Formula) Methane (CH4 ) Ethylene (C2 H2 ) Ammonia (NH3 ) Water (H2 O) Polar or Nonpolar? Melting Point( C) Boiling Point ( C) nonpolar nonpolar polar polar -182 -169 -78 0 -162 -104 -33 100 Q: Which compound in the Table 1.1 do you think is more polar, ammonia or water? | text | null |
L_0923 | inclined plane | T_4525 | An inclined plane is a simple machine that consists of a sloping surface connecting a lower elevation to a higher elevation. An inclined plane is one of six types of simple machines, and it is one of the oldest and most basic. In fact, two other simple machines, the wedge and the screw, are variations of the inclined plane. A ramp like the one in the Figure 1.1 is another example of an inclined plane. Inclined planes make it easier to move objects to a higher elevation. The sloping surface of the inclined plane supports part of the weight of the object as it moves up the slope. As a result, it takes less force to move the object uphill. The trade-off is that the object must be moved over a greater distance than if it were moved straight up to the higher elevation. | text | null |
L_0923 | inclined plane | T_4526 | The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of output force (the force put out by the machined) to input force (the force put into the machine). For an inclined plane, less force is put into moving an object up the slope than if the object were lifted straight up, so the mechanical advantage is greater than 1. The more gradual the slope of the inclined plane, the less input force is needed and the greater the mechanical advantage. Q: Which inclined plane pictured in the Figure 1.2 has a greater mechanical advantage? A: The inclined plane on the right has a more gradual slope, so it has a greater mechanical advantage. Less force is needed to move objects up the gentler slope, yet the objects attain the same elevation as they would if more force were used to push them up the steeper slope. | text | null |
L_0923 | inclined plane | T_4526 | The mechanical advantage of a simple machine is the factor by which it multiplies the force applied to the machine. It is the ratio of output force (the force put out by the machined) to input force (the force put into the machine). For an inclined plane, less force is put into moving an object up the slope than if the object were lifted straight up, so the mechanical advantage is greater than 1. The more gradual the slope of the inclined plane, the less input force is needed and the greater the mechanical advantage. Q: Which inclined plane pictured in the Figure 1.2 has a greater mechanical advantage? A: The inclined plane on the right has a more gradual slope, so it has a greater mechanical advantage. Less force is needed to move objects up the gentler slope, yet the objects attain the same elevation as they would if more force were used to push them up the steeper slope. | text | null |
L_0924 | inertia | T_4527 | Inertia is the tendency of an object to resist a change in its motion. All objects have inertia, whether they are stationary or moving. Inertia explains Newtons first law of motion, which states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Thats why Newtons first law of motion is sometimes called the law of inertia. Q: You probably dont realize it, but you experience inertia all the time, and you dont have to ride a skateboard. For example, think about what happens when you are riding in a car that stops suddenly. Your body moves forward on the seat and strains against the seat belt. Why does this happen? A: The brakes stop the car but not your body, so your body keeps moving forward because of inertia. | text | null |
L_0924 | inertia | T_4528 | The inertia of an object depends on its mass. Objects with greater mass also have greater inertia. It would be easier for Lauren to push just one of her cousins on her skateboard than both of them. With just one twin, there would be only about half as much mass on the skateboard, so there would be less inertia to overcome. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0924 | inertia | T_4529 | To change the motion of an object, inertia must be overcome by an unbalanced force acting on the object. The unbalanced force that starts Laurens cousins rolling along on the skateboard is applied by Lauren when she gives it a push. Once an object starts moving, inertia keeps it moving without any additional force being applied. In fact, it wont stop moving unless another unbalanced force opposes its motion. For example, Lauren can stop the rolling skateboard by moving to the other end and pushing in the opposite direction. Q: What if Lauren didnt stop the skateboard in this way? If it remained on a smooth, flat surface, would it just keep rolling forever? A: The inertia of the moving skateboard would keep it rolling forever if no other unbalanced force opposed its motion. However, another unbalanced force does act on the skateboard Q: What other force is acting on the skateboard? A: The other force is rolling friction between the skateboards wheels and the ground. The force of friction opposes the motion of the rolling skateboard and would eventually bring it to a stop without any help from Lauren. Friction opposes the motion of all moving objects, solike the skateboardall moving objects eventually stop moving even if no other forces oppose their motion. Later that day, Jonathan rode his skateboard and did some jumps. You can see him in the picture 1.2. When hes in the air, there is no rolling friction between his wheels and the ground, but another unbalanced force is acting on the skateboard and changing its motion. Q: What force is acting on the skateboard when it is in the air above the ground? And how will this force change the skateboards motion? A: The force of gravity is acting on the skateboard. It will pull the skateboard back down to the ground. Once its on the ground, friction will slow its motion. | text | null |
L_0925 | intensity and loudness of sound | T_4530 | Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined, in turn, by the intensity of the sound waves. Intensity is a measure of the amount of energy in sound waves. The unit of intensity is the decibel (dB). | text | null |
L_0925 | intensity and loudness of sound | T_4531 | The Figure 1.1 shows decibel levels of several different sounds. As decibel levels get higher, sound waves have greater intensity and sounds are louder. For every 10-decibel increase in the intensity of sound, loudness is 10 times greater. Therefore, a 30-decibel quiet room is 10 times louder than a 20-decibel whisper, and a 40-decibel light rainfall is 100 times louder than the whisper. High-decibel sounds are dangerous. They can damage the ears and cause loss of hearing. Q: How much louder than a 20-decibel whisper is the 60-decibel sound of a vacuum cleaner? A: The vacuum cleaner is 10,000 times louder than the whisper! | text | null |
L_0925 | intensity and loudness of sound | T_4532 | The intensity of sound waves determines the loudness of sounds, but what determines intensity? Intensity results from two factors: the amplitude of the sound waves and how far they have traveled from the source of the sound. Amplitude is a measure of the size of sound waves. It depends on the amount of energy that started the waves. Greater amplitude waves have more energy and greater intensity, so they sound louder. As sound waves travel farther from their source, the more spread out their energy becomes. You can see how this works in the Figure 1.2. As distance from the sound source increases, the area covered by the sound waves increases. The same amount of energy is spread over a greater area, so the intensity and loudness of the sound is less. This explains why even loud sounds fade away as you move farther from the source. Q: Why can low-amplitude sounds like whispers be heard only over short distances? A: The sound waves already have so little energy that spreading them out over a wider area quickly reduces their intensity below the level of hearing. | text | null |
L_0926 | internal combustion engines | T_4533 | A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the energy to do work. In a car, the engine does the work of providing kinetic energy that turns the wheels. The combustion engine in a car is a type of engine called an internal combustion engine. (Another type of combustion engine is an external combustion engine.) | text | null |
L_0926 | internal combustion engines | T_4534 | An internal combustion engine burns fuel internally, or inside the engine. This type of engine is found not only in cars but in most other motor vehicles as well. The engine works in a series of steps, which keep repeating. You can follow the steps in the Figure 1.1. 1. A mixture of fuel and air is pulled-into a cylinder through a valve, which then closes. 2. A piston inside the cylinder moves upward, compressing the fuel-air mixture in the closed cylinder. The mixture is now under a lot of pressure and very warm. 3. A spark from a spark plug ignites the fuel-air mixture, causing it to burn explosively within the confined space of the closed cylinder. 4. The pressure of the hot gases from combustion pushes the piston downward. 5. The piston moves up again, pushing exhaust gases out of the cylinder through another valve. 6. The piston moves downward again, and the cycle repeats. Q: The internal combustion engine converts thermal energy to another form of energy. Which form of energy is it? A: The engine converts thermal energy to kinetic energy, or the energy of a moving objectin this case, the moving piston. | text | null |
L_0926 | internal combustion engines | T_4535 | In a car, the piston in the engine is connected by the piston rod to the crankshaft. The crankshaft rotates when the piston moves up and down. The crankshaft, in turn, is connected to the driveshaft. When the crankshaft rotates, so does the driveshaft. The rotating driveshaft turns the wheels of the car. | text | null |
L_0926 | internal combustion engines | T_4536 | Most cars have at least four cylinders connected to the crankshaft. Their pistons move up and down in sequence, one after the other. A powerful car may have eight pistons, and some race cars may have even more. The more cylinders a car engine has, the more powerful its engine can be. | text | null |
L_0927 | international system of units | T_4537 | The example of the Mars Climate Orbiter shows the importance of using a standard system of measurement in science and technology. The measurement system used by most scientists and engineers is the International System of Units, or SI. There are a total of seven basic SI units, including units for length (meter) and mass (kilogram). SI units are easy to use because they are based on the number 10. Basic units are multiplied or divided by powers of ten to arrive at bigger or smaller units. Prefixes are added to the names of the units to indicate the powers of ten, as shown in the Table 1.1. Prefix kilo- (k) Multiply Basic Unit 1000 Basic Unit of Length = Meter (m) kilometer (km) = 1000 m Prefix deci- (d) centi- (c) milli- (m) micro- () nano- (n) Multiply Basic Unit 0.1 0.01 0.001 0.000001 0.000000001 Basic Unit of Length = Meter (m) decimeter (dm) = 0.1 m centimeter (cm) = 0.01 m millimeter (mm) = 0.001 m micrometer (m) = 0.000001 m nanometer (nm) = 0.000000001 m Q: What is the name of the unit that is one-hundredth (0.01) of a meter? A: The name of this unit is the centimeter. Q: What fraction of a meter is a decimeter? A: A decimeter is one-tenth (0.1) of a meter. | text | null |
L_0927 | international system of units | T_4538 | In the Table 1.2, two basic SI units are compared with their English system equivalents. You can use the information in the table to convert SI units to English units or vice versa. For example, from the table you know that 1 meter equals 39.37 inches. How many inches are there in 3 meters? 3 m = 3(39.37 in) = 118.11 in Measure Length Mass SI Unit meter (m) kilogram (kg) English Unit Equivalent 1 m = 39.37 in 1 kg = 2.20 lb Q: Rod needs to buy a meter of wire for a science experiment, but the wire is sold only by the yard. If he buys a yard of wire, will he have enough? (Hint: There are 36 inches in a yard.) A: Rod needs 39.37 inches (a meter) of wire, but a yard is only 36 inches, so if he buys a yard of wire he wont have enough. | text | null |
L_0928 | ionic bonding | T_4539 | An ionic bond is the force of attraction that holds together positive and negative ions. It forms when atoms of a metallic element give up electrons to atoms of a nonmetallic element. The Figure 1.1 shows how this happens. In row 1 of the Figure 1.1, an atom of sodium (Na) donates an electron to an atom of chlorine (Cl). By losing an electron, the sodium atom becomes a sodium ion. It now has more protons than electrons and a charge of +1. Positive ions such as sodium are given the same name as the element. The chemical symbol has a plus sign to distinguish the ion from an atom of the element. The symbol for a sodium ion is Na+ . By gaining an electron, the chlorine atom becomes a chloride ion. It now has more electrons than protons and a charge of -1. Negative ions are named by adding the suffix -ide to the first part of the element name. The symbol for chloride is Cl . Sodium and chloride ions have equal but opposite charges. Opposite electric charges attract each other, so sodium and chloride ions cling together in a strong ionic bond. You can see this in row 2 of the Figure 1.1. (Brackets separate the ions in the diagram to show that the ions in the compound do not actually share electrons.) When ionic bonds hold ions together, they form an ionic compound. The compound formed from sodium and chloride ions is named sodium chloride. It is commonly called table salt. | text | null |
L_0928 | ionic bonding | T_4540 | Ionic bonds form only between metals and nonmetals. Thats because metals want to give up electrons, and nonmetals want to gain electrons. Find sodium (Na) in the Figure 1.2. Sodium is an alkali metal in group 1. Like all group 1 elements, it has just one valence electron. If sodium loses that one electron, it will have a full outer energy level, which is the most stable arrangement of electrons. Now find fluorine (F) in the periodic table Figure gains one electron, it will also have a full outer energy level and the most stable arrangement of electrons. Q: Predict what other elements might form ionic bonds. A: Metals on the left and in the center of the periodic table form ionic bonds with nonmetals on the right of the periodic table. For example, alkali metals in group 1 form ionic bonds with halogen nonmetals in group 17. | text | null |
L_0928 | ionic bonding | T_4541 | It takes energy to remove valence electrons from an atom because the force of attraction between the negative electrons and the positive nucleus must be overcome. The amount of energy needed depends on the element. Less energy is needed to remove just one or a few valence electrons than many. This explains why sodium and other alkali metals form positive ions so easily. Less energy is also needed to remove electrons from larger atoms in the same group. For example, in group 1, it takes less energy to remove an electron from francium (Fr) at the bottom of the group than from lithium (Li) at the top of the group (see the Figure 1.2). In bigger atoms, valence electrons are farther from the nucleus. As a result, the force of attraction between the valence electrons and the nucleus is weaker. Q: What do you think happens when an atom gains an electron and becomes a negative ion? A: Energy is released when an atom gains an electron. Halogens release the most energy when they form ions. As a result, they are very reactive elements. | text | null |
L_0929 | ionic compounds | T_4542 | All compounds form when atoms of different elements share or transfer electrons. Compounds in which electrons are transferred from one atom to another are called ionic compounds. In this type of compound, electrons actually move between the atoms, rather than being shared between them. When atoms give up or accept electrons in this way, they become charged particles called ions. The ions are held together by ionic bonds, which form an ionic compound. Ionic compounds generally form between elements that are metals and elements that are nonmetals. For example, the metal calcium (Ca) and the nonmetal chlorine (Cl) form the ionic compound calcium chloride (CaCl2 ). In this compound, there are two negative chloride ions for each positive calcium ion. Because the positive and negative charges cancel out, an ionic compound is neutral in charge. Q: Now can you explain why calcium chloride prevents ice from forming on a snowy road? A: If calcium chloride dissolves in water, it breaks down into its ions (Ca2+ and Cl ). When water has ions dissolved in it, it has a lower freezing point. Pure water freezes at 0 C. With calcium and chloride ions dissolved in it, it wont freeze unless the temperature reaches -29 C or lower. | text | null |
L_0929 | ionic compounds | T_4543 | Many compounds form molecules, but ionic compounds form crystals instead. A crystal consists of many alternating positive and negative ions bonded together in a matrix. Look at the crystal of sodium chloride (NaCl) in the Figure bonds. Sodium chloride crystals are cubic in shape. Other ionic compounds may have crystals with different shapes. | text | null |
L_0929 | ionic compounds | T_4544 | Ionic compounds are named for their positive and negative ions. The name of the positive ion always comes first, followed by the name of the negative ion. For example, positive sodium ions and negative chloride ions form the compound named sodium chloride. Similarly, positive calcium ions and negative chloride ions form the compound named calcium chloride. Q: What is the name of the ionic compound that is composed of positive barium ions and negative iodide ions? A: The compound is named barium iodide. | text | null |
L_0929 | ionic compounds | T_4545 | The crystal structure of ionic compounds is strong and rigid. It takes a lot of energy to break all those ionic bonds. As a result, ionic compounds are solids with high melting and boiling points. You can see the melting and boiling points of several different ionic compounds in the Table 1.1. To appreciate how high they are, consider that the melting and boiling points of water, which is not an ionic compound, are 0 C and 100 C, respectively. Ionic Compound Sodium chloride (NaCl) Calcium chloride (CaCl2 ) Barium oxide (BaO) Iron bromide (FeBr3 ) Melting Point ( C) 801 772 1923 684 Boiling Point ( C) 1413 1935 2000 934 Solid ionic compounds are poor conductors of electricity. The strong bonds between their oppositely charged ions lock them into place in the crystal. Therefore, the charged particles cannot move freely and carry electric current, which is a flow of charge. But all that changes when ionic compounds dissolve in water. When they dissolve, they separate into individual ions. The ions can move freely, so they can carry current. Dissolved ionic compounds are called electrolytes. The rigid crystals of ionic compounds are brittle. They are more likely to break than bend when struck. As a result, ionic crystals tend to shatter easily. Try striking salt crystals with a hammer and youll find that they readily break into smaller pieces. Click image to the left or use the URL below. URL: | text | null |
L_0929 | ionic compounds | T_4546 | Ionic compounds have many uses. Some are shown in the Figure 1.2. Many ionic compounds are used in industry. The human body needs several ions for good health. Having low levels of the ions can endanger important functions such as heartbeat. Solutions of ionic compounds can be used to restore the ions. | text | null |
L_0930 | ions | T_4547 | The northern lights arent caused by atoms, because atoms are not charged particles. An atom always has the same number of electrons as protons. Electrons have an electric charge of -1 and protons have an electric charge of +1. Therefore, the charges of an atoms electrons and protons cancel out. This explains why atoms are neutral in electric charge. Q: What would happen to an atoms charge if it were to gain extra electrons? A: If an atom were to gain extra electrons, it would have more electrons than protons. This would give it a negative charge, so it would no longer be neutral. | text | null |
L_0930 | ions | T_4548 | Atoms cannot only gain extra electrons. They can also lose electrons. In either case, they become ions. Ions are atoms that have a positive or negative charge because they have unequal numbers of protons and electrons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine (see Figure 1.1). A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with an electric charge of -1. | text | null |
L_0930 | ions | T_4549 | Like fluoride, other negative ions usually have names ending in -ide. Positive ions, on the other hand, are just given the element name followed by the word ion. For example, when a sodium atom loses an electron, it becomes a positive sodium ion. The charge of an ion is indicated by a plus (+) or minus sign (-), which is written to the right of and just above the ions chemical symbol. For example, the fluoride ion is represented by the symbol F , and the sodium ion is represented by the symbol Na+ . If the charge is greater than one, a number is used to indicate it. For example, iron (Fe) may lose two electrons to form an ion with a charge of plus two. This ion would be represented by the symbol Fe2+ . This and some other common ions are listed with their symbols in the Table 1.1. Cations Name of Ion Calcium ion Hydrogen ion Iron(II) ion Iron(III) ion Chemical Symbol Ca2+ H+ Fe2+ Fe3+ Anions Name of Ion Chloride Fluoride Bromide Oxide Chemical Symbol Cl F Br O2 Q: How does the iron(III) ion differ from the iron(II) ion? A: The iron(III) ion has a charge of +3, so it has one less electron than the iron(II) ion, which has a charge of +2. Q: What is the charge of an oxide ion? How does its number of electrons compare to its number of protons? A: An oxide ion has a charge of -2. It has two more electrons than protons. | text | null |
L_0930 | ions | T_4550 | The process in which an atom becomes an ion is called ionization. It may occur when atoms are exposed to high levels of radiation. The radiation may give their outer electrons enough energy to escape from the attraction of the positive nucleus. However, most ions form when atoms transfer electrons to or from other atoms or molecules. For example, sodium atoms may transfer electrons to chlorine atoms. This forms positive sodium ions (Na+ ) and negative chloride ions (Cl ). Click image to the left or use the URL below. URL: | text | null |
L_0930 | ions | T_4551 | Ions are highly reactive, especially as gases. They usually react with ions of opposite charge to form neutral compounds. For example, positive sodium ions and negative chloride ions react to form the neutral compound sodium chloride, commonly known as table salt. This occurs because oppositely charged ions attract each other. Ions with the same charge, on the other hand, repel each other. Ions are also deflected by a magnetic field, as you saw in the opening image of the northern lights. | text | null |
L_0931 | isomers | T_4552 | Hydrocarbons are compounds that contain only carbon and hydrogen atoms. The smallest hydrocarbon, methane (CH4 ), contains just one carbon atom and four hydrogen atoms. Larger hydrocarbons contain many more. Hydro- carbons with four or more carbon atoms can have different shapes. Although they have the same chemical formula, with the same numbers of carbon and hydrogen atoms, they form different compounds, called isomers. Isomers are compounds whose properties are different because their atoms are bonded together in different arrangements. | text | null |
L_0931 | isomers | T_4553 | The smallest hydrocarbon that has isomers is butane, which has just four carbon atoms. In the Figure 1.1 you can see structural formulas for normal butane (or n-butane) and its only isomer, named iso-butane. Both molecules have four carbon atoms as well as ten hydrogen atoms (C4 H10 ), but the atoms are arranged differently in the two compounds. In n-butane, all four carbon atoms are lined up in a straight chain. In iso-butane, one of the carbon atoms branches off from the main chain. The next smallest hydrocarbon is pentane, which has five carbon atoms and twelve hydrogen atoms (C5 H12 ). Pentane has three isomers: n-pentane, iso-pentane, and neo-pentane. Their structural formulas are shown in the images below. Look at the carbon atoms in each isomer. In n-pentane (see Figure 1.2), the carbon atoms form a straight chain. In iso-pentane (see Figure 1.3), one carbon atom branches off from the main chain. In neo-pentane (see Figure 1.4), two carbon atoms branch off from the main chain. | text | null |
L_0931 | isomers | T_4554 | Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. | text | null |
L_0931 | isomers | T_4554 | Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. | text | null |
L_0931 | isomers | T_4554 | Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. | text | null |
L_0931 | isomers | T_4554 | Butane has only two isomers and pentane has just three, but some hydrocarbons have many more isomers than these. As you increase the number of carbon atoms in a hydrocarbon, the number of isomers quickly increases. For example, heptane, with seven carbon atoms, has nine isomers; and dodecane, with twelve carbon atoms, has 355 isomers. Some hydrocarbons with many more carbon atoms have billions of isomers! Q: Why does the number of carbon atoms in a hydrocarbon determine how many isomers it has? A: The more carbon atoms there are, the greater the number of possible arrangements of carbon atoms. | text | null |
L_0931 | isomers | T_4555 | Because isomers are different compounds, they have different properties. Generally, branched-chain isomers have lower boiling and melting points than straight-chain isomers. For example, the boiling and melting points of iso- butane are -12 C and -160 C, respectively, compared with 0 C and -138 C for n-butane. The more branching there is, the lower the boiling and melting points are. Q: The boiling point of n-pentane is 36 C. Predict the boiling points of iso-pentane and neo-pentane. A: The boiling point of iso-pentane is 28 C, and the boiling point of neo-pentane is 10 C. | text | null |
L_0932 | isotopes | T_4556 | All atoms of the same element have the same number of protons, but some may have different numbers of neutrons. For example, all carbon atoms have six protons, and most have six neutrons as well. But some carbon atoms have seven or eight neutrons instead of the usual six. Atoms of the same element that differ in their numbers of neutrons are called isotopes. Many isotopes occur naturally. Usually one or two isotopes of an element are the most stable and common. Different isotopes of an element generally have the same physical and chemical properties. Thats because they have the same numbers of protons and electrons. Click image to the left or use the URL below. URL: | text | null |
L_0932 | isotopes | T_4557 | Hydrogen is an example of an element that has isotopes. Three isotopes of hydrogen are modeled in the Figure hydrogen. Some hydrogen atoms have one neutron as well. These atoms are the isotope named deuterium. Other hydrogen atoms have two neutrons. These atoms are the isotope named tritium. Q: The mass number of an atom is the sum of its protons and neutrons. What is the mass number of each isotope of hydrogen shown above? A: The mass numbers are: hydrogen = 1, deuterium = 2, and tritium = 3. | text | null |
L_0932 | isotopes | T_4558 | For most elements other than hydrogen, isotopes are named for their mass number. For example, carbon atoms with the usual 6 neutrons have a mass number of 12 (6 protons + 6 neutrons = 12), so they are called carbon-12. Carbon atoms with 7 neutrons have an atomic mass of 13 (6 protons + 7 neutrons = 13). These atoms are the isotope called carbon-13. Q: Some carbon atoms have 8 neutrons. What is the name of this isotope of carbon? A: Carbon atoms with 8 neutrons have an atomic mass of 14 (6 protons + 8 neutrons = 14), so this isotope of carbon is named carbon-14. | text | null |
L_0932 | isotopes | T_4559 | Atoms need a certain ratio of neutrons to protons to have a stable nucleus. Having too many or too few neutrons relative to protons results in an unstable, or radioactive, nucleus that will sooner or later break down to a more stable form. This process is called radioactive decay. Many isotopes have radioactive nuclei, and these isotopes are referred to as radioisotopes. When they decay, they release particles that may be harmful. This is why radioactive isotopes are dangerous and why working with them requires special suits for protection. The isotope of carbon known as carbon-14 is an example of a radioisotope. In contrast, the carbon isotopes called carbon-12 and carbon-13 are stable. | text | null |
L_0933 | kinetic energy | T_4560 | Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energyfrom atoms in matter to stars in outer space. Things with kinetic energy can do work. For example, the spinning saw blade in the photo above is doing the work of cutting through a piece of metal. | text | null |
L_0933 | kinetic energy | T_4561 | The amount of kinetic energy in a moving object depends directly on its mass and velocity. An object with greater mass or greater velocity has more kinetic energy. You can calculate the kinetic energy of a moving object with this equation: Kinetic Energy (KE) = 12 mass velocity2 This equation shows that an increase in velocity increases kinetic energy more than an increase in mass. If mass doubles, kinetic energy doubles as well, but if velocity doubles, kinetic energy increases by a factor of four. Thats because velocity is squared in the equation. Lets consider an example. The Figure 1.1 shows Juan running on the beach with his dad. Juan has a mass of 40 kg and is running at a velocity of 1 m/s. How much kinetic energy does he have? Substitute these values for mass and velocity into the equation for kinetic energy: m2 2 KE = 12 40 kg (1 m s ) = 20 kg s2 = 20 N m, or 20 J Notice that the answer is given in joules (J), or N m, which is the SI unit for energy. One joule is the amount of energy needed to apply a force of 1 Newton over a distance of 1 meter. What about Juans dad? His mass is 80 kg, and hes running at the same velocity as Juan (1 m/s). Because his mass is twice as great as Juans, his kinetic energy is twice as great: m2 2 KE = 12 80 kg (1 m s ) = 40 kg s2 = 40 N m, or 40 J Q: What is Juans kinetic energy if he speeds up to 2 m/s from 1 m/s? A: By doubling his velocity, Juan increases his kinetic energy by a factor of four: m2 2 KE = 12 40 kg (2 m s ) = 80 kg s2 = 80 N m, or 80 J | text | null |
L_0934 | kinetic theory of matter | T_4562 | Energy is the ability to cause changes in matter. For example, your body uses chemical energy when you lift your arm or take a step. In both cases, energy is used to move matteryou. Any matter that is moving has energy just because its moving. The energy of moving matter is called kinetic energy. Scientists think that the particles of all matter are in constant motion. In other words, the particles of matter have kinetic energy. The theory that all matter consists of constantly moving particles is called the kinetic theory of matter. | text | null |
L_0934 | kinetic theory of matter | T_4563 | Differences in kinetic energy explain why matter exists in different states. Particles of matter are attracted to each other, so they tend to pull together. The particles can move apart only if they have enough kinetic energy to overcome this force of attraction. Its like a tug of war between opposing sides, with the force of attraction between particles on one side and the kinetic energy of individual particles on the other side. The outcome of the war determines the state of matter. If particles do not have enough kinetic energy to overcome the force of attraction between them, matter exists as a solid. The particles are packed closely together and held rigidly in place. All they can do is vibrate. This explains why solids have a fixed volume and a fixed shape. If particles have enough kinetic energy to partly overcome the force of attraction between them, matter exists as a liquid. The particles can slide past one another but not pull apart completely. This explains why liquids can change shape but have a fixed volume. If particles have enough kinetic energy to completely overcome the force of attraction between them, matter exists as a gas. The particles can pull apart and spread out. This explains why gases have neither a fixed volume nor a fixed shape. Look at the Figure 1.1. It sums up visually the relationship between kinetic energy and state of matter. Q: How could you use a bottle of cola to demonstrate these relationships between kinetic energy and state of matter? A: You could shake a bottle of cola and then open it. Shaking causes carbon dioxide to come out of the cola solution and change to a gas. The gas fizzes out of the bottle and spreads into the surrounding air, showing that its particles have enough kinetic energy to spread apart. Then you could tilt the open bottle and pour out a small amount of the cola on a table, where it will form a puddle. This shows that particles of the liquid have enough kinetic energy to slide over each other but not enough to pull apart completely. If you do nothing to the solid glass of the cola bottle, it will remain the same size and shape. Its particles do not have enough energy to move apart or even to slide over each other. | text | null |
L_0935 | law of conservation of momentum | T_4564 | When skater 2 runs into skater 1, hes going faster than skater 1 so he has more momentum. Momentum is a property of a moving object that makes it hard to stop. Its a product of the objects mass and velocity. At the moment of the collision, skater 2 transfers some of his momentum to skater 1, who shoots forward when skater 2 runs into him. Whenever an action and reaction such as this occur, momentum is transferred from one object to the other. However, the combined momentum of the objects remains the same. In other words, momentum is conserved. This is the law of conservation of momentum. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0935 | law of conservation of momentum | T_4565 | The Figure 1.1 shows how momentum is conserved in the two colliding skaters. The total momentum is the same after the collision as it was before. However, after the collision, skater 1 has more momentum and skater 2 has less momentum than before. Q: What if two skaters have a head-on collision? Do you think momentum is conserved then? A: As in all actions and reactions, momentum is also conserved in a head-on collision. | text | null |
L_0936 | law of reflection | T_4566 | Reflection is one of several ways that light can interact with matter. Light reflects off surfaces such as mirrors that do not transmit or absorb light. When light is reflected from a smooth surface, it may form an image. An image is a copy of an object that is formed by reflected (or refracted) light. Q: Is an image an actual object? If not, what is it? A: No, an image isnt an actual object. It is focused rays of light that make a copy of an object, like a picture projected on a screen. | text | null |
L_0936 | law of reflection | T_4567 | If a surface is extremely smooth, as it is in a mirror, then the image formed by reflection is sharp and clear. This is called regular reflection (also called specular reflection). However, if the surface is even slightly rough or bumpy, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Q: Look at the boats and their images in the Figure 1.1. Which one represents regular reflection, and which one represents diffuse reflection? A: Reflection of the boat on the left is regular reflection. The water is smooth and the image is sharp and clear. Reflection of the boat on the right is diffuse reflection. The water has ripples and the image is blurry and wavy. In the Figure 1.2, you can see how both types of reflection occur. Waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. | text | null |
L_0936 | law of reflection | T_4567 | If a surface is extremely smooth, as it is in a mirror, then the image formed by reflection is sharp and clear. This is called regular reflection (also called specular reflection). However, if the surface is even slightly rough or bumpy, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Q: Look at the boats and their images in the Figure 1.1. Which one represents regular reflection, and which one represents diffuse reflection? A: Reflection of the boat on the left is regular reflection. The water is smooth and the image is sharp and clear. Reflection of the boat on the right is diffuse reflection. The water has ripples and the image is blurry and wavy. In the Figure 1.2, you can see how both types of reflection occur. Waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. | text | null |
L_0936 | law of reflection | T_4568 | One thing is true of both regular and diffuse reflection. The angle at which the reflected rays leave the surface is equal to the angle at which the incident rays strike the surface. This is known as the law of reflection. The law is illustrated in the Figure 1.3. | text | null |
L_0937 | lens | T_4569 | A lens is a transparent object with one or two curved surfaces. It is typically made of glass (or clear plastic in the case of a contact lens). A lens refracts, or bends, light and forms an image. An image is a copy of an objected formed by the refraction (or reflection) of visible light. The more curved the surface of a lens is, the more it refracts the light that passes through it. There are two basic types of lenses: concave and convex. The two types of lenses have different shapes, so they bend light and form images in different ways. | text | null |
L_0937 | lens | T_4570 | A concave lens is thicker at the edges than it is in the middle. You can see the shape of a concave lens in the Figure Note that the image formed by a concave lens is on the same side of the lens as the object. It is also smaller than the object and right-side up. However, it isnt a real image. It is a virtual image. Your brain tricks you into seeing an image there. The light rays actually pass through the glass to the other side and spread out in all directions. | text | null |
L_0937 | lens | T_4571 | A convex lens is thicker in the middle than at the edges. You can see the shape of a convex lens in the Figure 1.2. A convex lens causes rays of light to converge, or meet, at a point called the focus (F). A convex lens forms either a real or virtual image. It depends on how close the object is to the lens relative to the focus. Q: An example of a convex lens is a hand lens. Which of the three convex lens diagrams in the Figure 1.2 shows how a hand lens makes an image? A: Youve probably looked through a hand lens before. If you have, then you know that the image it produces is right-side up. Therefore, the first diagram must show how a hand lens makes an image. Its the only one that produces a right-side up image. | text | null |
L_0938 | lever | T_4572 | A lever is a simple machine consisting of a bar that rotates around a fixed point. The fixed point of a lever is called the fulcrum. Like other machines, a lever makes work easier by changing the force applied to the machine or the distance over which the force is applied. How does a hammer make it easier to pull a nail out of a board? First, it changes the direction of the force applied to the hammerthe hand pushes down on the handle while the claw end of the hammer head pulls up. Often, you can push down with more force than you can push up because you can put your own weight behind it. The hammer also increases the strength of the force that is applied to it. It easily pulls the nail out of the board, which you couldnt do with your hands alone. On the other hand, the hammer decreases the distance over which the force is applied. The hand pushing down on the handle moves the handle over a distance of several inches, whereas the hammer pulls up on the nail only an inch or two. Q: Where is the fulcrum of the hammer when it is used to pull a nail out of a board? In other words, around what point does the hammer rotate? A: The fulcrum is the point where the head of the hammer rests on the surface of the board. | text | null |
L_0938 | lever | T_4573 | Other levers change force or distance in different ways than a hammer removing a nail. How a lever changes force or distance depends on the location of the input and output forces relative to the fulcrum. The input force is the force applied by the user to the lever. The output force is the force applied by the lever to the object. Based on the location of input and output forces, there are three basic types of levers, called first-class, second-class, and third-class levers. The Table 1.1 describes the three classes. Class of Lever Example of Lever in This Class First class Location of Input & Output Forces & Fulcrum* Ideal Mechanical Advantage Change in Direction of Force? Seesaw 1 <1 >1 yes yes yes Second class Wheelbarrow >1 no Third class Hockey stick <1 no = fulcrum I = input force O = output force The Table 1.1 includes the ideal mechanical advantage of each class of lever. The mechanical advantage is the factor by which a machine changes the input force. The ideal mechanical advantage is the increase or decrease in force that would occur if there were no friction to overcome in the use of the machine. Because all machines must overcome some friction, the ideal mechanical advantage is always somewhat greater than the actual mechanical advantage of the machine as it is used in the real world. Q: Which class of lever is a hammer when it is used to pry a nail out of a board? What is its mechanical advantage? A: To pry a nail out of a board, the fulcrum is located between the input and output forces. Therefore, when a hammer is used in this way it is a first class lever. The fulcrum is closer to the output force than the input force, so the mechanical advantage is >1. In other words, the hammer increases the force applied to it, making it easier to pry the nail out of the board. | text | null |
L_0938 | lever | T_4574 | All three classes of levers make work easier, but they do so in different ways. When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with first-class levers. When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second-class and third-class levers. When the input force is applied farther from the fulcrum than the output force is, the output force is greater than the input force, and the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers. When the input force is applied closer to the fulcrum than the output force is, the output force is less than the input force, and the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers. When the input and output forces are the same distance from the fulcrum, the output force equals the input force, and the ideal mechanical advantage is 1. This occurs only with first some first-class levers. | text | null |
L_0938 | lever | T_4575 | You may be wondering why you would use a third-class lever when it doesnt change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. The output end of the lever must move faster than the input end in order to cover the greater distance. Q: A broom is a third-class lever when it is used to sweep a floor (see the Figure 1.1), so the output end of the lever moves faster than the input end. Why is this useful? A: By moving more quickly over the floor, the broom does the work faster. | text | null |
L_0939 | light | T_4576 | Electromagnetic waves are waves that carry energy through matter or space as vibrating electric and magnetic fields. Electromagnetic waves have a wide range of wavelengths and frequencies. Sunlight contains the complete range of wavelengths of electromagnetic waves, which is called the electromagnetic spectrum. The Figure 1.1 shows all the waves in the spectrum. | text | null |
L_0939 | light | T_4577 | Light includes infrared light, visible light, and ultraviolet light. As you can see from the Figure 1.1, light falls roughly in the middle of the electromagnetic spectrum. It has shorter wavelengths and higher frequencies than microwaves, but not as short and high as X rays. Q: Which type of light do you think is harmful to the skin? A: Waves of light with the highest frequencies have the most energy and are harmful to the skin. Use the electro- magnetic spectrum in the Figure 1.1 to find out which of the three types of light have the highest frequencies. | text | null |
L_0939 | light | T_4578 | Light with the longest wavelengths is called infrared light. The term infrared means below red. Infrared light is the range of light waves that have longer wavelengths and lower frequencies than red light in the visible range of light waves. The sun gives off infrared light as do flames and living things. You cant see infrared light waves, but you can feel them as heat. But infrared cameras and night vision goggles can detect infrared light waves and convert them to visible images. | text | null |
L_0939 | light | T_4579 | The only light that people can see is called visible light. This light consists of a very narrow range of wavelengths that falls between infrared light and ultraviolet light. Within the visible range, we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength (see Figure 1.2). When all of the wavelengths of visible light are combined, as they are in sunlight, visible light appears white. | text | null |
L_0939 | light | T_4580 | Light with wavelengths shorter than visible light is called ultraviolet light. The term ultraviolet means above violet. Ultraviolet light is the range of light waves that have shorter wavelengths and higher frequencies than violet light in the visible range of light. With higher frequencies than visible light, ultraviolet light has more energy. It can be used to kill bacteria in food and to sterilize surgical instruments. The human skin also makes vitamin D when it is exposed to ultraviolet light. Vitamin D, in turn, is needed for strong bones and teeth. Too much exposure to ultraviolet light can cause sunburn and skin cancer. As the slip, slop, slap slogan suggests, you can protect your skin from ultraviolet light by wearing clothing that covers your skin, applying sunscreen to any exposed areas, and wearing a hat to protect your head from exposure. The SPF, or sun-protection factor, of sunscreen gives a rough idea of how long it protects the skin from sunburn (see Figure 1.3). A sunscreen with a higher SPF value protects the skin longer. Sunscreen must be applied liberally and often to be effective, and no sunscreen is completely waterproof. Q: You should apply sunscreen even on cloudy days. Can you explain why? A: Ultraviolet light can travel through clouds, so it can harm unprotected skin even on cloudy days. | text | null |
L_0940 | lipid classification | T_4581 | Lipids are one of four classes of biochemical compounds, which are compounds that make up living things and carry out life processes. (The other three classes of biochemical compounds are carbohydrates, proteins, and nucleic acids.) Living things use lipids to store energy. Lipids are also the major components of cell membranes in living things. Types of lipids include fats and oils. Fats are solid lipids that animals use to store energy. Oils are liquid lipids that plants use to store energy. Q: Can you name some lipids that are fats? What are some lipids that are oils? A: Lipids that are fats include butter and the fats in meats. Lipids that are oils include olive oil and vegetable oil. Examples of both types of lipids are pictured in the Figure 1.1. | text | null |
L_0940 | lipid classification | T_4582 | Lipids consist only or mainly of carbon, hydrogen, and oxygen. Both fats and oils are made up of long chains of carbon atoms that are bonded together. These chains are called fatty acids. Fatty acids may be saturated or (A) The white bands on these lamb chops are fat. (B) The yellow liquid in this bottle is olive oil. unsaturated. In the Figure 1.2 you can see structural formulas for two small fatty acids, one saturated and one unsaturated. Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. Unsaturated fatty acids have at least one double bond between carbon atoms. As a result, some carbon atoms are not bonded to as many hydrogen atoms as possible. They are unsaturated with hydrogens. Unsaturated fatty acids are found in oils. Q: Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid molecule contain? What else is different about the two molecules? A: The saturated fatty acid molecule has 12 hydrogen atoms. This is as many hydrogen atoms as can possibly be bonded to carbon atoms in this molecule. The unsaturated fatty acid molecule has 10 hydrogen atoms, or two less than the maximum possible number. The saturated fatty acid has only single bonds between its carbon atoms. The unsaturated fatty acid has a double bond between two of its carbon atoms. | text | null |
L_0940 | lipid classification | T_4582 | Lipids consist only or mainly of carbon, hydrogen, and oxygen. Both fats and oils are made up of long chains of carbon atoms that are bonded together. These chains are called fatty acids. Fatty acids may be saturated or (A) The white bands on these lamb chops are fat. (B) The yellow liquid in this bottle is olive oil. unsaturated. In the Figure 1.2 you can see structural formulas for two small fatty acids, one saturated and one unsaturated. Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. Unsaturated fatty acids have at least one double bond between carbon atoms. As a result, some carbon atoms are not bonded to as many hydrogen atoms as possible. They are unsaturated with hydrogens. Unsaturated fatty acids are found in oils. Q: Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid molecule contain? What else is different about the two molecules? A: The saturated fatty acid molecule has 12 hydrogen atoms. This is as many hydrogen atoms as can possibly be bonded to carbon atoms in this molecule. The unsaturated fatty acid molecule has 10 hydrogen atoms, or two less than the maximum possible number. The saturated fatty acid has only single bonds between its carbon atoms. The unsaturated fatty acid has a double bond between two of its carbon atoms. | text | null |
L_0940 | lipid classification | T_4583 | Some lipids contain the element phosphorus as well as carbon, hydrogen, and oxygen. These lipids are called phospholipids. Two layers of phospholipid molecules make up the cell membranes of living things. In the Figure One end of each phospholipid molecule is polar, so it has a partial electric charge. Water is also polar and has electrically charged ends, so it is attracted to the oppositely charged end of a phospholipid molecule. This end of the phospholipid molecule is described as hydrophilic, which means water loving. The other end of each phospholipid molecule is nonpolar and has no electric charge. This end of the phospho- lipid molecule repels polar water and is described as hydrophobic, or water hating. In the Figure 1.3, the hydrophilic ends of the phospholipid molecules are on the outsides of the cell membrane, and the hydrophobic ends are on the inside of the cell membrane. This arrangement of phospholipids allows some substances to pass through the cell membrane while keeping other substances out. | text | null |
L_0942 | longitudinal wave | T_4586 | A longitudinal wave is a type of mechanical wave. A mechanical wave is a wave that travels through matter, called the medium. In a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave travels. You can see this in the Figure 1.1. The persons hand pushes and pulls on one end of the spring. The energy of this disturbance passes through the coils of the spring to the other end. Click image to the left or use the URL below. URL: | text | null |
L_0942 | longitudinal wave | T_4587 | Notice in the Figure 1.1 that the coils of the spring first crowd closer together and then spread farther apart as the wave passes through them. Places where particles of a medium crowd closer together are called compressions, and places where the particles spread farther apart are called rarefactions. The more energy the wave has, the closer together the particles are in compressions and the farther apart they are in rarefactions. | text | null |
L_0942 | longitudinal wave | T_4588 | Earthquakes cause longitudinal waves called P waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions away from the disturbance. P waves are modeled in the Figure Q: Where are the compressions and rarefactions of the medium in this model of P waves? A: The compressions are the places where the vertical lines are closest together. The rarefactions are the places where the vertical lines are farthest apart. | text | null |
L_0943 | magnetic field reversal | T_4589 | Earths magnetic poles have switched places repeatedly in the past. As you can see in the Figure 1.1, each time the switch occurred, Earths magnetic field was reversed. The magnetic field is the region around a magnet over which it exerts magnetic force. We think of todays magnetic field direction as normal, but thats only because its what were used to. | text | null |
L_0943 | magnetic field reversal | T_4590 | Scientists dont know for certain why magnetic reversals occur, but there is hard evidence that they have for hundreds of millions of years. The evidence comes from rocks on the ocean floor. Look at Figure 1.2. They show the same ridge on the ocean floor during different periods of time. A. At the center of the ridge, hot magma pushes up through the crust and hardens into rock. Once the magma hardens, the alignment of magnetic domains in the rock is frozen in place forever. Magnetic domains are regions in the rocks where all the atoms are lined up and pointing toward Earths north magnetic pole. B. The newly hardened rock is gradually pushed away from the ridge in both directions as more magma erupts and newer rock forms. The alignment of magnetic domains in this new rock is in the opposite direction, showing that a magnetic reversal has occurred. C. A magnetic reversal occurs again. It is frozen in rock to document the change. Rock samples from many places on the ocean floor show that the north and south magnetic poles reversed hundreds of times over the last 330 million years. The last reversal was less than a million years ago. | text | null |
L_0944 | magnets | T_4591 | A magnet is an object that attracts certain materials such as iron. Youre probably familiar with common bar magnets, like the one shown in the Figure 1.1. Like all magnets, this bar magnet has north and south magnetic poles. The red end of the magnet is the north pole and the blue end is the south pole. The poles are regions where the magnet is strongest. The poles are called north and south because they always line up with Earths north-south axis if the magnet is allowed to move freely. (Earths axis is the imaginary line around which the planet rotates.) Q: What do you suppose would happen if you cut the bar magnet pictured in the Figure 1.1 along the line between the north and south poles? A: Both halves of the magnet would also have north and south poles. If you cut each of the halves in half, all those pieces would have north and south poles as well. Pieces of a magnet always have both north and south poles no matter how many times you cut the magnet. | text | null |
L_0944 | magnets | T_4592 | The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. | text | null |
L_0944 | magnets | T_4592 | The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. | text | null |
L_0944 | magnets | T_4592 | The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. | text | null |
L_0946 | mechanical advantage | T_4596 | How much a machine changes the input force is its mechanical advantage. Mechanical advantage is the ratio of the output force to the input force, so it can be represented by the equation: Actual Mechanical Advantage = Output force Input force Note that this equation represents the actual mechanical advantage of a machine. The actual mechanical advantage takes into account the amount of the input force that is used to overcome friction. The equation yields the factor by which the machine changes the input force when the machine is actually used in the real world. | text | null |
L_0946 | mechanical advantage | T_4597 | It can be difficult to measure the input and output forces needed to calculate the actual mechanical advantage of a machine. Generally, an unknown amount of the input force is used to overcome friction. Its usually easier to measure the input and output distances than the input and output forces. The distance measurements can then be used to calculate the ideal mechanical advantage. The ideal mechanical advantage represents the change in input force that would be achieved by the machine if there were no friction to overcome. The ideal mechanical advantage is always greater than the actual mechanical advantage because all machines have to overcome friction. Ideal mechanical advantage can be calculated with the equation: Ideal Mechanical Advantage = Input Distance Output Distance | text | null |
L_0946 | mechanical advantage | T_4598 | Look at the ramp in the Figure 1.1. A ramp is a type of simple machine called an inclined plane. It can be used to raise an object off the ground. The input distance is the length of the sloped surface of the ramp. This is the distance over which the input force is applied. The output distance is the height of the ramp, or the vertical distance the object is raised. For this ramp, the input distance is 6 m and the output distance is 2 meters. Therefore, the ideal mechanical advantage of this ramp is: Input distance Ideal Mechanical Advantage = Output distance = 62 m m =3 An ideal mechanical advantage of 3 means that the ramp ideally (in the absence of friction) multiplies the input force by a factor of 3. The trade-off is that the input force must be applied over a greater distance than the object is lifted. Q: Assume that another ramp has a sloping surface of 8 m and a vertical height of 4 m. What is the ideal mechanical advantage of this ramp? A: The ramp has an ideal mechanical advantage of: Ideal Mechanical Advantage = 84 m m =2 | text | null |
L_0946 | mechanical advantage | T_4599 | Many machinesincluding inclined planes such as rampsincrease the strength of the force put into the machine but decrease the distance over which the force is applied. Other machines increase the distance over which the force is applied but decrease the strength of the force. Still other machines change the direction of the force, with or without also increasing its strength or distance. Which way a machine works determines its mechanical advantage, as shown in the Table 1.1. Strength of Force increases decreases stays the same (changes direction only) Distance Over Force is Applied decreases increases stays the same which Mechanical Advantage Example >1 <1 =1 ramp hammer flagpole pulley | text | null |
L_0947 | mechanical wave | T_4600 | The waves in the picture above are examples of mechanical waves. A mechanical wave is a disturbance in matter that transfers energy through the matter. A mechanical wave starts when matter is disturbed. A source of energy is needed to disturb matter and start a mechanical wave. Q: Where does the energy come from in the water wave pictured above? A: The energy comes from the falling droplets of water, which have kinetic energy because of their motion. | text | null |
L_0947 | mechanical wave | T_4601 | The energy of a mechanical wave can travel only through matter. The matter through which the wave travels is called the medium (plural, media). The medium in the water wave pictured above is water, a liquid. But the medium of a mechanical wave can be any state of matter, even a solid. Q: How do the particles of the medium move when a wave passes through them? A: The particles of the medium just vibrate in place. As they vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on. Particles of the medium dont actually travel along with the wave. Only the energy of the wave travels through the medium. | text | null |
L_0947 | mechanical wave | T_4602 | There are three types of mechanical waves: transverse, longitudinal, and surface waves. They differ in how particles of the medium move. You can see this in the Figure 1.1. In a transverse wave, particles of the medium vibrate up and down perpendicular to the direction of the wave. In a longitudinal wave, particles of the medium vibrate back and forth parallel to the direction of the wave. In a surface wave, particles of the medium vibrate both up and down and back and forth, so they end up moving in a circle. Q: How do you think surface waves are related to transverse and longitudinal waves? A: A surface wave is combination of a transverse wave and a longitudinal wave. | text | null |
L_0949 | mendeleevs periodic table | T_4606 | For many years, scientists looked for a good way to organize the elements. This became increasingly important as more and more elements were discovered. An ingenious method of organizing elements was developed in 1869 by a Russian scientist named Dmitri Mendeleev, who is pictured 1.1. Mendeleevs method of organizing elements was later revised, but it served as a basis for the method that is still used today. Mendeleev was a teacher as well as a chemist. He was writing a chemistry textbook and wanted to find a way to organize the 63 known elements so it would be easier for students to learn about them. He made a set of cards of the elements, similar to a deck of playing cards. On each card, he wrote the name of a different element, its atomic mass, and other known properties. Mendeleev arranged and rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by increasing atomic mass. Q: What is atomic mass? Why might it be a good basis for organizing elements? A: Atomic mass is the mass of one atom of an element. It is about equal to the mass of the protons plus the neutrons in an atom. It is a good basis for organizing elements because each element has a unique number of protons and atomic mass is an indirect way of organizing elements by number of protons. | text | null |
L_0949 | mendeleevs periodic table | T_4607 | You can see how Mendeleev organized the elements in the Figure 1.2. From left to right across each row, elements are arranged by increasing atomic mass. Mendeleev discovered that if he placed eight elements in each row and then continued on to the next row, the columns of the table would contain elements with similar properties. He called the columns groups. They are sometimes called families, because elements within a group are similar but not identical to one another, like people in a family. Mendeleevs table of the elements is called a periodic table because of its repeating pattern. Anything that keeps repeating is referred to as periodic. Other examples of things that are periodic include the monthly phases of the moon and the daily cycle of night and day. The term period refers to the interval between repetitions. For example, the moons phases repeat every four weeks. In a periodic table of the elements, the periods are the rows of the table. In Mendeleevs table, each period contains eight elements, and then the pattern repeats in the next row. | text | null |
L_0949 | mendeleevs periodic table | T_4608 | Did you notice the blanks in Mendeleevs table? They are spaces that Mendeleev left blank for elements that had not yet been discovered when he created his table. He predicted that these missing elements would eventually be discovered. Based on their position in the table, he even predicted their properties. For example, he predicted a missing element in row 5 of group III. He also predicted that the missing element would have an atomic mass of 68 and be a relatively soft metal like other elements in this group. Scientists searched for the missing element, and they found it just a few years later. They named the new element gallium. Scientists searched for the other missing elements in Mendeleevs table and eventually found all of them. An important measure of a good model is its ability to make accurate predictions. This makes it a useful model. Clearly, Mendeleevs periodic table was a useful model. It helped scientists discover new elements and made sense of those that were already known. | text | null |
L_0950 | metallic bonding | T_4609 | Metallic bonds are forces of attraction between positive metal ions and the valence electrons that are constantly moving around them (see the Figure 1.1). The valence electrons include their own and those of other, nearby ions of the same metal. The valence electrons of metals move freely in this way because metals have relatively low electronegativity, or attraction to electrons. The positive metal ions form a lattice-like structure held together by all the metallic bonds. Click image to the left or use the URL below. URL: Q: Why do metallic bonds form only in elements that are metals? Why dont similar bonds form in elements that are nonmetals? A: Metal atoms readily give up valence electrons and become positive ions whenever they form bonds. When nonmetals bond together, the atoms share valence electrons and do not become ions. For example, when oxygen atoms bond together they form oxygen molecules in which two oxygen atoms share two pairs of valence electrons equally, so neither atom becomes charged. | text | null |
L_0950 | metallic bonding | T_4610 | The valence electrons surrounding metal ions are constantly moving. This makes metals good conductors of electricity. The lattice-like structure of metal ions is strong but quite flexible. This allows metals to bend without breaking. Metals are both ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Q: Look at the metalworker in the Figure 1.2. Hes hammering a piece of hot iron in order to shape it. Why doesnt the iron crack when he hits it? A: The iron ions can move within the sea of electrons around them. They can shift a little closer together or farther apart without breaking the metallic bonds between them. Therefore, the metal can bend rather than crack when the hammer hits it. | text | null |
L_0950 | metallic bonding | T_4610 | The valence electrons surrounding metal ions are constantly moving. This makes metals good conductors of electricity. The lattice-like structure of metal ions is strong but quite flexible. This allows metals to bend without breaking. Metals are both ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Q: Look at the metalworker in the Figure 1.2. Hes hammering a piece of hot iron in order to shape it. Why doesnt the iron crack when he hits it? A: The iron ions can move within the sea of electrons around them. They can shift a little closer together or farther apart without breaking the metallic bonds between them. Therefore, the metal can bend rather than crack when the hammer hits it. | text | null |
L_0951 | metalloids | T_4611 | Metalloids are the smallest class of elements. (The other two classes of elements are metals and nonmetals). There are just six metalloids. In addition to silicon, they include boron, germanium, arsenic, antimony, and tellurium. Metalloids fall between metals and nonmetals in the periodic table. They also fall between metals and nonmetals in terms of their properties. Q: How does the position of an element in the periodic table influence its properties? A: Elements are arranged in the periodic table by their atomic number, which is the number of protons in their atoms. Atoms are neutral in electric charge, so they always have the same number of electrons as protons. It is the number of electrons in the outer energy level of atoms that determines most of the properties of elements. | text | null |
L_0951 | metalloids | T_4612 | How metalloids behave in chemical interactions with other elements depends mainly on the number of electrons in the outer energy level of their atoms. Metalloids have from three to six electrons in their outer energy level. Boron, pictured in the Figure 1.1, is the only metalloid with just three electrons in its outer energy level. It tends to act like metals by giving up its electrons in chemical reactions. Metalloids with more than four electrons in their outer energy level (arsenic, antimony, and tellurium) tend to act like nonmetals by gaining electrons in chemical reactions. Those with exactly four electrons in their outer energy level (silicon and germanium) may act like either metals or nonmetals, depending on the other elements in the reaction. | text | null |
L_0951 | metalloids | T_4613 | Most metalloids have some physical properties of metals and some physical properties of nonmetals. For example, metals are good conductors of both heat and electricity, whereas nonmetals generally cannot conduct heat or electricity. And metalloids? They fall between metals and nonmetals in their ability to conduct heat, and if they can conduct electricity, they usually can do so only at higher temperatures. Metalloids that can conduct electricity at higher temperatures are called semiconductors. Silicon is an example of a semiconductor. It is used to make the tiny electric circuits in computer chips. You can see a sample of silicon and a silicon chip in the Figure 1.2. Metalloids tend to be shiny like metals but brittle like nonmetals. Because they are brittle, they may chip like glass or crumble to a powder if struck. Other physical properties of metalloids are more variable, including their boiling and melting points, although all metalloids exist as solids at room temperature. Click image to the left or use the URL below. URL: | text | null |
L_0952 | metals | T_4614 | Metals are elements that can conduct electricity. They are one of three classes of elements (the other two classes are nonmetals and metalloids). Metals are by far the largest of the three classes. In fact, most elements are metals. All of the elements on the left side and in the middle of the periodic table, except for hydrogen, are metals. There are several different types of metals, including alkali metals in group 1 of the periodic table, alkaline Earth metals in group 2, and transition metals in groups 3-12. The majority of metals are transition metals. | text | null |
L_0952 | metals | T_4615 | Elements in the same class share certain basic similarities. In addition to conducting electricity, many metals have several other shared properties, including those listed below. Metals have relatively high melting points. This explains why all metals except for mercury are solids at room temperature. Most metals are good conductors of heat. Thats why metals such as iron, copper, and aluminum are used for pots and pans. Metals are generally shiny. This is because they reflect much of the light that strikes them. The mercury pictured above is very shiny. The majority of metals are ductile. This means that they can be pulled into long, thin shapes, like the aluminum electric wires pictured in the Figure 1.1. Metals tend to be malleable. This means that they can be formed into thin sheets without breaking. An example is aluminum foil, also pictured in the Figure 1.1. Q: The defining characteristic of metals is their ability to conduct electricity. Why do you think metals have this property? A: The properties of metalsas well as of elements in the other classesdepend mainly on the number and arrangement of their electrons. | text | null |
L_0952 | metals | T_4616 | To understand why metals can conduct electricity, consider the metal lithium as an example. An atom of lithium is modeled below. Look at lithiums electrons. There are two electrons at the first energy level. This energy level can hold only two electrons, so it is full in lithium. The second energy level is another story. It can hold a maximum of eight electrons, but in lithium it has just one. A full outer energy level is the most stable arrangement of electrons. Lithium would need to gain seven electrons to fill its outer energy level and make it stable. Its far easier for lithium to give up its one electron in energy level 2, leaving it with a full outer energy level (now level 1). Electricity is a flow of electrons. Because lithium (like most other metals) easily gives up its extra electron, it is a good conductor of electricity. This tendency to give up electrons also explains other properties of metals such as lithium. | text | null |
L_0953 | microwaves | T_4617 | Electromagnetic waves carry energy through matter or space as vibrating electric and magnetic fields. Electromag- netic waves have a wide range of wavelengths and frequencies. The complete range is called the electromagnetic spectrum. The Figure 1.1 shows all the waves of the spectrum. The waves used in radar guns are microwaves. | text | null |
L_0953 | microwaves | T_4618 | Find the microwave in the Figure 1.1. A microwave is an electromagnetic wave with a relatively long wavelength and low frequency. Microwaves are often classified as radio waves, but they have higher frequencies than other radio waves. With higher frequencies, they also have more energy. Thats why microwaves are useful for heating food in microwave ovens. Microwaves have other important uses as well, including cell phone transmissions and radar. These uses are described below. Click image to the left or use the URL below. URL: | text | null |
L_0953 | microwaves | T_4619 | Cell phone signals are carried through the air as microwaves. You can see how this works in the Figure 1.2. A cell phone encodes the sounds of the callers voice in microwaves by changing the frequency of the waves. This is called frequency modulation. The encoded microwaves are then sent from the phone through the air to a cell tower. From the cell tower, the waves travel to a switching center. From there they go to another cell tower and from the tower to the receiver of the person being called. The receiver changes the encoded microwaves back to sounds. Q: Cell towers reach high above the ground. Why do you think such tall towers are used? A: Microwaves can be interrupted by buildings and other obstructions, so cell towers must be placed high above the ground to prevent the interruption of cell phone signals. | text | null |
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