text: Although Force Recon has never been part of the United States Special Operations Command, their missions slightly differentiate themselves from other United States Special Operations Forces units. Colloquially, they are specialized in all tactical areas of warfare. Force Recon will train with other Special Operations forces, such as, United States Navy SEALs, United States Army Special Forces, and United States Air Force Pararescue, in order to master all skill sets. The Marine Corps has seen fit to train versatile specialists rather than specialists in individual areas of combat.


title: United States Marine Corps Force Reconnaissance

text: Their reconnoitering roles (whether amphibious or ground) include preliminary (or "pre–D-Day") and post-assault reconnaissance. Some examples are:


text: Black operations are the missions that require direct action (DA). They are the opposite of green operations missions, where the Force Recon operators "look for trouble." Depending on the situation and the target location, the FORECON operators usually conduct direct action missions within the artillery and naval gun support fan; these operations demonstrate "small-scale" shock and awe.


text: Examples are the seizures and occupation of gas/oil platforms (GOPLAT) and the visit, board, search, and seizure (VBSS) of ships during Maritime Interdiction Operations (MIO), as well as orchestrating close air support, a vital skill exercised in DA missions; Force Recon operators forward observe from static positions and spider holes for artillery and naval gunfire support, or ordnance and payload delivery.


text: They provide personal security detail (PSD) for critically important personnel. They are capable of performing In-Extremis Hostage Rescue (IHR) but this is no longer a Force Recon mission task. The Maritime Special Purpose Force (MSPF) was designed for IHR missions for the Marine Expeditionary Force's (MEF) subordinate Marine Expeditionary Unit (Special Operations Capable) (MEU (SOC)) in its stead.


text: In the past, early Force Reconnaissance companies in the Marine Corps had made numerous titular changes to its table of organization (T/O), so much so that it can be difficult to describe its primary command structure in detail. However, the companies initially were designed to function under the echelon of the Navy/Marine force commanders (e.g. under the direct operational control of the Commander, Amphibious Task Force (CATF) and Landing Force (CLF), and Fleet Marine Force) during amphibious landing operations or expeditionary engagements—to provide timely intelligence without exhausting their reconnaissance assets from the Marine Division without hampering their valuable support to its infantry regiments.


text: Due to these changes, FORECON has been detached and reported to multiple commanders of Marine divisions, the Command Elements (CE) of the Marine Air-Ground Task Forces, and the immediate commander of the Marine Expeditionary Force (MEF). They were re-organized or reserved for 'special reconnaissance' assignments that would otherwise help shape the outcome of his battlefield. These companies, for a few times in their existence, had either folded into the Marine Division, its Regiment's Recon Battalions, or dissolved entirely to only resurface during conflicts, or when other similar reasons had arisen.


text: After the creation of Marine Special Operations Command (MARSOC) on August 11, 2006, it marked the United States Marine Corps' first commitment to the United States Special Operations Command (USSOCOM). By February 2006, 2nd FORECON deactivated its command. The most experienced operators were selected to fill the ranks for the newly established Marine Special Operations Battalions' (MSOBs) teams. A month later in January, 1st FORECON met the same fate. The remaining Marines in both Force Recon companies molded into new "D" companies within the Division Recon Battalions, forming the Deep Reconnaissance Platoons (DRPs). The DRPs are designed to maintain and preserve the 'deep reconnaissance' assets to the MAGTF commanders.


text: In October 2008, by the direction of the Commandant of the Marine Corps (CMC), the D companies within both 1st and 2nd Reconnaissance Battalions were redesignated as "Force Reconnaissance" companies and assigned operational control to the Marine Expeditionary Force (MEF) accordingly, particularly the I MEF and II MEF. These companies will assume the traditional deep reconnaissance and supportive arms mission set and will deploy in support of current directive required by the United States Marine Corps. Since that time, the Marine Corps has also stood up Force Reconnaissance Company, III MEF in Okinawa, Japan.


text: The three Force Reconnaissance companies of I, II, and III MEF are currently the only active components of force-"level" reconnaissance; whereas the 3rd and 4th FORECON are the Selected Reserve force reconnaissance assets available to augment and reinforce the Fleet Marine Force. In the Marine Corps Reserve, the FORECON are separate units reporting directly to the 4th Marine Division Commanding General (4th MarDiv CG), unless mobilized and ordered detached to a Gaining Force Commander. Additionally, as separate units, the FORECON are not part of 4th Reconnaissance Battalion, which is itself a separate unit reporting directly to the 4th MarDiv CG.


text: Each Force Reconnaissance company is basically the same; they all contain a command element and Force Recon platoons. Each company is commanded by a company commander and his executive officer.


text: The historical roots of 'Force Recon' companies can be traced back to the antecedent Amphibious Reconnaissance Battalion, whose numerous pre-D–Day reconnoitering of enemy beaches during the Pacific campaigns of World War II proved the vitality of the Fleet Marine Force's amphibious reconnaissance doctrine. This unique unit reported directly to the landing force commander, providing him important intelligence at his disposal.


text: Formed initially as a company-size element from the Observer Group, under the command of Major James L. Jones, they were amongst the first—along with the early Navy Combat Demolition Units (the predecessor to the Underwater Demolition Teams [i.e., the Navy SEALs])—to embark from submarines; most of their missions complemented those of the NCDU and the UDT. The 'amphibious reconnaissance' doctrine clearly outlined that the recon Marines' duties consisted of scouting the littoral areas, or beachhead, and inland; to test the soil permeability for a possible beach landing; to clear any obstacles that may hinder an amphibious assault; and to observe any sign of enemy activity. The Navy UDT were tasked with providing the same, but from off the coastline to the littoral, or adjacent beach areas.


text: Jones and his recon Marines scouted the Japanese-fortified beaches and observed the terrain, materials or other entities, primarily reporting to the force commander of any vital intelligence of mission-oriented importance. Although Jones's Marines were all skilled surface swimmers, they usually inserted by boats—mostly due to the multiple radios (primary and contingent) they carried, as relaying communication to the landing force commander was paramount, and as a timely means of sending in a platoon-sized element with heavy firepower (mortars, machineguns, etc.) at their disposal since they were greatly outnumbered and isolated from other major Marine forces, which were still embarked on the destroyer-transport ships.


text: By the end of World War II, the Amphib Recon Battalion terminated its command; its Marines either filled the ranks of other infantry platoons, or folded into the Scout (Tank) companies, and the newly formed division reconnaissance companies. This force-level reconnaissance element was not re-established until the early 1950s, when the Amphibious Reconnaissance Battalions were assembled for preliminary operations in Korea. Their efforts proved that gaining the knowledge of the enemy before a major operation was crucial to safeguarding the men, and provided better operational planning.


text: The Korean War introduced the new concept of using rotary-wing aircraft to the Marine Corps in combat employment for logistics and rapid troop transport. Also, the atomic age was emerging and caused concern among the military leaders. The Commandant of the Marine Corps, General Lemuel Shepherd created a test unit, the Marine Corps Test Unit 1 (MCTU #1), to research and experiment on new and improved combat tactics and on methods to prepare the Marine Corps to operate strategically, in concert with or against, the use of nuclear weapons.


text: Many of the conceptual ideas for Force Recon were pioneered by Major Bruce F. Meyers, the test unit's "Reconnaissance/Pathfinder Project Officer" from MCTU #1's Plans and Development (P&D) Section. His position can be seen as an unillustrated subsidiary to an 'operations' (G-6) and 'training' (G-7) officer. Major Meyers tested various innovative techniques for the 'Recon Platoon' and evaluated their results for use in parachuting and pathfinding missions, in addition to using its heliborne and aircraft wing assets to add 'deeper' reconnaissance penetration capabilities. This new-found capability gave reconnaissance Marines the advantage of operating further behind enemy lines.


text: The MCTU#1's Reconnaissance Platoon, commanded by Captain Joseph Taylor, founded and adopted the more modern 'force reconnaissance' doctrine, methods which were instrumented by Major Meyers. They were developing and performing innovative clandestine insertion methods before the Navy SEALs, and the Army's "Green Berets", such as the submarine locking -in and -out methods, and underwater "blow-and-go" ascents.


text: The USMC concluded that parachute reconnaissance and pathfinding capabilities would exist at force level, the Fleet Marine Force (the highest command echelon of the United States Marine Corps). At first, the concept was to be formed into a "Force Recon Battalion"—this battalion would have as many 'force recon' companies as there were division-wing MAGTFs in the Marine operating forces. Recognizing the limited budget during the fiscal year of 1957, it was instead recommended that it be formed at company-sized elements for the west and east coast. In July 1957, The MCTU#1 was amalgamated into the existing 1st Amphibious Reconnaissance Battalion. The next day, the battalion cased its colors and redesignated it as 1st Force Reconnaissance Company. Although the test unit was no longer operating, Meyers continued to research and test more innovative methods.


text: Major Meyers and his top swimmers and senior officers of the company would test and train in submarine lock-in and -out methods and ascending techniques. After being cross-trained by the Navy's Master Divers, they learned the operation of the early rebreather systems, and advanced open water swimming. Meyers understood that his recon Marines would be operating 50 to 150 miles away from their littoral or operating area, or from any naval support. In order to get his Marines out of a "hot" area, extraction techniques needed to be developed. Bruce Meyer's 1st FORECON, along with 1st Recon Company and 1st Marine Aircraft Wing were aware of the McGuire and STABO systems that were used by the United States Army's Special Forces, though they agreed that they had defects and disadvantages. Instead, the Marine Corps created a system that was a more simplified rig that had greater capacity, the Special Personnel Insertion and Extraction (SPIE) rig.


text: The CIA's highly secretive Special Activities Division (SAD), and more specifically its elite Special Operations Group (SOG), recruit operators from Marine Force Recon. In addition, joint Force Recon and CIA operations go back to the famed Military Assistance Command, Vietnam – Studies and Observations Group (MACV-SOG) MACV-SOG group during the Vietnam War and still exist to this day.


text: The Reconnaissance/Surveillance Section of the Weapons Planning Group, Landing Force Development Center at Quantico introduced Force Recon to new technological methods of achieving their objective. Many of its tests and evaluations resembled the tests of MCTU #1. However, MCTU #1 were testing methods of inserting reconnaissance teams "deep" into the battlefield. The Weapons Planning Group (Code 121) provided the equipment that would become instrumental to recon Marines. Beacons for helicopter guidance, laser designators for the guidance of ordnance, laser rangefinders, and many more were tested.


text: During the Vietnam War, one of the reconnaissance officers of Code 121, then-Major Alex Lee, brought most of his testing experience to 3rd Force Reconnaissance Company when he was assigned as the commanding officer from 1969 to 1970. He formed Force Recon's missions that are still distinct today: remote sensor operations. The Surveillance and Reconnaissance Center (SRC), predecessor to the Surveillance, Reconnaissance, and Intelligence Group (SRIG), was formed within the III Marine Amphibious Force (IIId MAF). The obsolete pathfinding operations were taken over by the newer beacons and homing devices.


text: 3rd Force Reconnaissance Company was activated, trained, fought and deactivated during the Vietnam War. Activated in September 1965 as one of the first group of add-on units to meet demands of operations in Vietnam, the company formed at Camp Lejeune, N.C. and satellite on Second Force Reconnaissance Company that was under strength due to the demands for trained Force Recon Marines assigned to First Force in country. Facilities, cadre and equipment for training were provided by Second Force.


text: Volunteers were solicited from throughout the Marine Corps and the first four months were devoted to bringing the company up to strength in personnel. Beginning in January 1966 all operational personnel departed Camp Lejeune to train in the Caribbean and Panama. Returning to North Carolina in March, final preparations were carried out to meet the projected deployment date in May 1966. The expected deployment of the entire company did not occur, but a two platoon detachment embarked on the USS Boxer, transited through the Suez Canal, and arrived in country in time to be introduced to combat in Operation Hastings as part of The Special Landing Force in early July 1966.


text: The company (-) dropped to a not combat ready readiness status. Headquarters Marine Corps transferred several Officers and numerous Staff Non Commissioned Officers immediately after the detachment departed. In mid-June the company (-) was alerted to deploy immediately. Due to the reduced personnel readiness status, HQMC changed the deployment plan and ordered that a platoon be assigned to deploy with First Battalion, 26th Marines that had been activated at Camp Pendleton. The remainder of the company was ordered to move to Camp Pendleton to refit.


text: At the conclusion of Hastings the detachment was attached to Third Reconnaissance Battalion that had just arrived in Phu Bai from DaNang, having been replaced by the First Reconnaissance Battalion that had just begun arriving with the First Marine Division. Shortly, they were joined by the platoon that had come in country with 1/26.


text: They patrolled in Thua Thien Province until early January, 1967, when a task organized Special Purpose group carried out a prisoner rescue attempt. The remainder were sent to Khe Sanh where they developed the intelligence of a large enemy buildup, that was the prelude to The Hill Fights that occurred in April 1967.


text: Reunited, what was left of the three platoons, returned to Phu Bai to await the arrival of the company(-). Having been brought up to strength and operational readiness, the company was reunited on April 27, 1967, just in time for the NVA offensive to seize Quang Tri Province. The logistics element arrive at the "Ramp" at Dong Ha just in time for the opening salvos of the NVA artillery attacks that would continue daily until late Autumn.


text: The operational element experienced a mortar attack in Phu Bai at the same time resulting in several shrapnel wounds, only one of which, required evacuation. The new arrivals were integrated with combat veterans and the entire eighteen teams conducted a zone reconnaissance in the Cobi Than Tan Valley east of Hue City before displacing to Dong Ha.


text: Upon arrival at Dong Ha in early May the Commanding Officer assumed command of Third Recon Battalion (Forward), which had reconnaissance responsibility for all of Quang Tri Province except the Khe Sanh TAOR (Tactical Area of Operations). The company patrolled the area north of Highway nine to the DMZ, while the Battalion Company was targeted south of Highway Nine to the Thua Thien border. Occasional circumstances caused deviation from that concept, but, for the most part, those deviations were rare. Third Force continued that operational commitment until the Third Division left country in November 1969.


text: Third Force was placed under command of The Third Marine Expeditionary Force and operated in general support of IIId MAF until deactivated in mid-1970.


text: Training within the Company is outlined by the Mission Training Plan (MTP). It is used in conjunction with the training and exercises that are conducted by the Marine Expeditionary Units for their "Special Operations Capable" certification. It follows a systematic approach to training, and the emphasis is to "train as they expect to fight".


text: The Mission Training Plan has five phases, and is based on a two-year platoon cycle. Training is ongoing and continuous, and functions as if it were a loop. Before FORECON operators are "Special Operations Capable" they follow the Company's MTP, which underlines the training protocol of the Pre-deployment Training Program (PTP).


text: The Marine candidates who had passed the initial yet vigorous indoctrination exam must undergo and complete a series of courses required for the designated MOS 0326 [formerly "8654"], "Reconnaissance Marine, Parachutist/Combatant Diver Qualified," known as the 'accession pipeline.'


text: Their courses to its various schools are intertwined with the Pre-deployment Training Program (PTP), a training protocol of the Fleet Marine Force–its task forces–that are conducted yearly in a perpetual, continuous cycle. The reconnaissance Marines within FORECON community are unique in that it is the volition of the individual Marine to remain another two-year detachment to the Force Reconnaissance Company. Those that had chosen to remain in the company will proceed to the advanced course of instructions, and again during the next FMF rotational training cycle, and forth. This is due in respects to their status of having already completed and qualified in the appropriate course required for MOS 0321; which otherwise, the initial training, e.g. the accession pipeline, are reserved for the candidates.


text: The first phase in FORECON's Mission Training Plan takes place within the MEU's Initial Training Phase.


text: During the "Individual Training Phase", the candidates are undergoing the accession pipeline to become qualified MOS 0321 (Reconnaissance Marine). After further training, the already-billeted Force Recon operators (who had already completed the required courses in the accession pipeline [BRC, parachutist and diving, and SERE/HRP courses]) attain MOS 0326 (Reconnaissance Marine, parachute and combatant diver qualified) and may continue to remain with FORECON after the three-year rotation cycle. They may be selected for additional advanced cross-service training from other schools provided by the Special Operations Forces (SOF) units. Although these specialized schools are not necessarily required, they are highly encouraged.


text: Many Marine Corps 'training liaisons' represent the Marines at many cross-services schools, to ensure training slots and openings are met and filled by the Marines that requested, or were recommended, for advanced training. Some of these courses may not be able to facilitate the Marine students; the instructors of these schools resort to complement the Marines' requested syllabus by designing similar subsidiary courses. This argument becomes clear on whether Marines may, or may not, actually attend the Basic Underwater Demolition/SEAL training (BUD/S). Nonetheless, in the past, selected operators within Force Recon had attended the courses of instructions provided by BUD/S Instructors and their completion is documented in their military Service Record Book (SRB) or Officer Qualification Record (OQR).


text: The Training Cell (T-Cell) is regulated by the experienced staff non-commissioned officers (SNCOs) of FMF Recon company's Operations Section (S-3). This removes the responsibility of coordinating training from the platoon headquarters, and permits them to train with their men (rather than to just oversee the training).


text: An additional and no less important advantage to the T-Cell is that it acts as a training ground for future platoon sergeants. Those assigned to the T-Cell are all highly trained and experienced operators. Some have deployed as platoon sergeants, and some have not. Experienced FORECON operators within T-Cell monitor, evaluate and improve the training to ensure that exercises meet real-world conditions.


text: Other training packages are available to mold the Marines into a fully functional Recon unit, including long range patrolling in desert areas, such as Twentynine Palms or MCAS Yuma, mountainous terrain and other environments relevant in peacetime or conflict. At the end of Phase 2 Training, the platoon is completely stood up in all aspects of the "long-range" reconnaissance mission. More importantly, they have spent 6 months of 'platoon-oriented' training together.


text: This six-month training phase emphasizing more in the direct action, or "black operations". It is conducted by the Special Operations Training Group (SOTG). This phase takes place during the MEU's PTP Intermediate Training Phase. These courses involves both aspects of maritime and urbanized environments and how to apply close quarters combat and science in demolition, gas/oil platform (GOPLAT) training, cordon and search, Visit, Board, Search, and Seizure (VBSS), shipboard assaults training and humanitarian operations. The recon operators get the chance to train in unfamiliar urban areas and maritime structures.


text: Once the SOC Certification Final Training Phase is finished, the MEU with the detached Force Recon platoon as a functional special operations "capable" force. Then they sail on a six-month deployment. This long deployment is known as the 'Deployment Phases' to Force Recon, they sail from either three locations, off the east or west coast, or Okinawa. The I MEF on the west would deploy its Marine Expeditionary Units (MEUs) to the western Pacific and the II MEF's MEUs on the east coast sails across the Atlantic Ocean to either the Mediterranean Sea or the Persian Gulf. The III MEF's 31st MEU in Okinawa is to be used as a contingency for reinforced support of an area spanning from southwest Asia to the central Pacific. The III MEF is the only MEF of the FMF that is permanently fully deployed at all times.


text: While Force Recon is afloat, they still remain focused on their self-disciplined training sessions. They conduct small arms live fire training on the deck of the ships and physical fitness training. In many cases, foreign maritime forces alike participate in joint exercises or training maneuvers, such as the Royal Thai Marine Corps, British Royal Marines, and Australian Forces. But while they may be training, the MEU are capable of projecting fully forward deployed operational task forces. Thus, epitomizing the infamous Marine Corps slogan, ""force-in-readiness"."


text: The last phase is the post-deployment phase. After 18 months of training and deployment, the platoon is granted 30 days of military leave. Once a Force Recon operator has finished deployment, they have a decision to make. What makes Force Recon unique from Division Recon, and the other SOFs, is the career style that is being placed in the Force Recon company structure. They can choose to stay with the Force Recon Company and continue their assignment with the MEU, recycling its loop cycle; or they can get release from the FORECON company and go back to their original assignment, whether administration, motor transport, or infantry. However, on average, approximately 50% of the platoon will leave, their time in Force having expired.


text: The primary weapons used by both Division and FMF Recon assets are typically the same standard-issued weapons in the arsenal of the Marine Corps. However, since Force Recon's missions are directly involved in parachuting and underwater insertions, they demand weapons and equipment that are essential to their job. Their equipment reflects on which ever tasks that have been assigned by the MAGTF, MEF, or MEU commander; either direct action (black) or deep recon (green) operations.


text: Some equipment only fits the needs for one particular mission over another. There is however some equipment that is used for both black and green operations, and these pieces of gear are usually combat vests, flak and armor jackets (or systems), and harnesses for use in hasty extraction measures.


text: Particularly during green operations, these missions normally encompass surveillance and reconnaissance. The equipment items carried into the field are usually cameras, scopes, and most importantly communications. Two recon Marines serve as radiomen in the team. Each team/platoon often brings two field radios that are able to withstand the elements of seawater, and rugged patrolling as they tread inland—if one radio fails, they resort to the supplemental radio. This is to ensure that vital information can always be sent to the commander, and to the S-3/S-6 shop, or similar intelligence collection agencies. More common in today's infrastructure, much of the intelligence-gathered information is sent to and processed by the Marine Expeditionary Force's "Surveillance, Reconnaissance, and Intelligence Group" (SRIG).


text: For black operations, the Marines carry weapons that are more of the close-quarter combative use; grenades, carbine rifles, sub-machine guns (SMGs), and any tool to use for breaching barricades and doors. They can be equipped with laser designating devices to "paint" their targets with laser-guiding coordinates to deliver payload to un-expecting targets. Since they are "bringing the fight to the enemy", they do not rely on camouflage as stealthy action is not a factor in these situations.


text: Throughout training and real life operations, jet fins, snorkels and low-volume double lens dive masks are used. In addition to the SCUBA equipment used in amphibious mission-essential tasks, Force Recon maintains and operates parachutes. This is the main difference and separation from Division Reconnaissance—all FORECON operators are required to be parachutists. The parachutist equipment is stored in the Force Reconnaissance's Parachute Loft.


text: The parachute is one of the trademarks of Force Recon, throughout its existence the operators have extensively used a wide variety of parachutes. In the mid-1950s, they used the T-10, then later adopting the Capewell canopy release which provided a cut-away to reduce the deadly effect of drag. The T-10 became the most frequented parachute; which had two variants, one for low-level static line (LLSL) and the other for military free fall (MFF) descends. They had numerous parachutes listed under the Table of Equipment (T/E) that had been contained in the Paraloft. Even in its formative days in the Marine Corps Test Unit#1, the operators and testers of the Naval Parachute Unit (NPU) at El Centro had tested and sported numerous parachutes, adding modifications and suggestions that soon were adopted by other parachutists. By the 1990s, the MC-4 and MC-5 ram air parachutes became the feasible choice, as it allows more detailed and accurate landing in smaller areas, easy to control—especially during oscillation of the canopy. Plus, it was formed to modulate between the LLSL and MFF without having to consort to a different pack.


text: These are parachutes that are still contained in the T/E of the Parachute Loft, however some may not be currently in use:


text: The Parachutist Individual Equipment Kit (PIEK) contains all the Force Recon's parachutist clothing and equipment assigned by Force Recon's Paraloft. They are used for the high-altitude MFFs (HAHO or HALO) and LLSL parachute operations. Due to extreme cold encountered during high altitude parachute operations, the parachutist must have protection from the environment.


text: The Force Recon operators are equipped with a complete equipment lowering system for both LLSL and MFF parachute operations. It allows them carry various configurations of all their individual mission-essential equipment, usually contained within their Flyer's Kitbag. The Single Action Release Personal Equipment Lowering Equipment (SARPELS) provides easy access to their weapons and equipment upon parachute landing and has a single-action release capability. It can be front or rear mounted, whichever is preferred. Once they have descended to about above the surface, they use the SARPEL to release their gear (weapons/kitbag), dropping it below them while still attached to their harness by a rope. It is used to minimize injuries in landing due to heavy load of equipment. The parachutists must maneuver themselves in order not to drop onto their gear during parachute landing falls.


text: The 24th MEU 2nd Force Reconnaissance Company won the 2010 Annual Warrior Competition against tactical units from all over the world.


text: Realizing it is my choice and my choice alone to be a Reconnaissance Marine, I accept all challenges involved with this profession. Forever shall I strive to maintain the tremendous reputation of those who went before me.


text: Exceeding beyond the limitations set down by others shall be my goal. Sacrificing personal comforts and dedicating myself to the completion of the reconnaissance mission shall be my life. Physical fitness, mental attitude, and high ethics—The title of Recon Marine is my honor.


text: Conquering all obstacles, both large and small, I shall never quit. To quit, to surrender, to give up is to fail. To be a Recon Marine is to surpass failure; To overcome, to adapt and to do whatever it takes to complete the mission.


text: On the battlefield, as in all areas of life, I shall stand tall above the competition. Through professional pride, integrity, and teamwork, I shall be the example for all Marines to emulate.


text: Never shall I forget the principles I accepted to become a Recon Marine. Honor, Perseverance, Spirit and Heart. A Recon Marine can speak without saying a word and achieve what others can only imagine.


title: Alkali metal

text: The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.


title: Alkali metal

text: The alkali metals are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation by atmospheric moisture and oxygen (and in the case of lithium, nitrogen). Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.


title: Alkali metal

text: All of the discovered alkali metals occur in nature as their compounds: in order of abundance, sodium is the most abundant, followed by potassium, lithium, rubidium, caesium, and finally francium, which is very rare due to its extremely high radioactivity; francium occurs only in minute traces in nature as an intermediate step in some obscure side branches of the natural decay chains. Experiments have been conducted to attempt the synthesis of ununennium (Uue), which is likely to be the next member of the group; none were successful. However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements; even if it does turn out to be an alkali metal, it is predicted to have some differences in physical and chemical properties from its lighter homologues.


title: Alkali metal

text: Most alkali metals have many different applications. One of the best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks, of which caesium atomic clocks form the basis of the second. A common application of the compounds of sodium is the sodium-vapour lamp, which emits light very efficiently. Table salt, or sodium chloride, has been used since antiquity. Lithium finds use as a psychiatric medication and as an anode in lithium batteries. Sodium, potassium and lithium are essential elements, having major biological roles as electrolytes, and although the other alkali metals are not essential, they also have various effects on the body, both beneficial and harmful.


title: Alkali metal

text: Sodium compounds have been known since ancient times; salt (sodium chloride) has been an important commodity in human activities, as testified by the English word "salary", referring to "salarium", money paid to Roman soldiers for the purchase of salt. While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence which led him to suggest the fundamental difference of sodium and potassium salts in 1702, and Henri-Louis Duhamel du Monceau was able to prove this difference in 1736. The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus Antoine Lavoisier did not include either alkali in his list of chemical elements in 1789.


title: Alkali metal

text: Pure potassium was first isolated in 1807 in England by Humphry Davy, who derived it from caustic potash (KOH, potassium hydroxide) by the use of electrolysis of the molten salt with the newly invented voltaic pile. Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium's extreme reactivity. Potassium was the first metal that was isolated by electrolysis. Later that same year, Davy reported extraction of sodium from the similar substance caustic soda (NaOH, lye) by a similar technique, demonstrating the elements, and thus the salts, to be different.


title: Alkali metal

text: Petalite (Li Al SiO) was discovered in 1800 by the Brazilian chemist José Bonifácio de Andrada in a mine on the island of Utö, Sweden. However, it was not until 1817 that Johan August Arfwedson, then working in the laboratory of the chemist Jöns Jacob Berzelius, detected the presence of a new element while analysing petalite ore. This new element was noted by him to form compounds similar to those of sodium and potassium, though its carbonate and hydroxide were less soluble in water and more alkaline than the other alkali metals. Berzelius gave the unknown material the name ""lithion"/"lithina"", from the Greek word "λιθoς" (transliterated as "lithos", meaning "stone"), to reflect its discovery in a solid mineral, as opposed to potassium, which had been discovered in plant ashes, and sodium, which was known partly for its high abundance in animal blood. He named the metal inside the material ""lithium"". Lithium, sodium, and potassium were part of the discovery of periodicity, as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner in 1850 as having similar properties.


title: Alkali metal

text: Rubidium and caesium were the first elements to be discovered using the spectroscope, invented in 1859 by Robert Bunsen and Gustav Kirchhoff. The next year, they discovered caesium in the mineral water from Bad Dürkheim, Germany. Their discovery of rubidium came the following year in Heidelberg, Germany, finding it in the mineral lepidolite. The names of rubidium and caesium come from the most prominent lines in their emission spectra: a bright red line for rubidium (from the Latin word "rubidus", meaning dark red or bright red), and a sky-blue line for caesium (derived from the Latin word "caesius", meaning sky-blue).


title: Alkali metal

text: Around 1865 John Newlands produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to the octaves of music, where notes an octave apart have similar musical functions. His version put all the alkali metals then known (lithium to caesium), as well as copper, silver, and thallium (which show the +1 oxidation state characteristic of the alkali metals), together into a group. His table placed hydrogen with the halogens.


title: Alkali metal

text: After 1869, Dmitri Mendeleev proposed his periodic table placing lithium at the top of a group with sodium, potassium, rubidium, caesium, and thallium. Two years later, Mendeleev revised his table, placing hydrogen in group 1 above lithium, and also moving thallium to the boron group. In this 1871 version, copper, silver, and gold were placed twice, once as part of group IB, and once as part of a "group VIII" encompassing today's groups 8 to 11. After the introduction of the 18-column table, the group IB elements were moved to their current position in the d-block, while alkali metals were left in "group IA". Later the group's name was changed to "group 1" in 1988. The trivial name "alkali metals" comes from the fact that the hydroxides of the group 1 elements are all strong alkalis when dissolved in water.


title: Alkali metal

text: There were at least four erroneous and incomplete discoveries before Marguerite Perey of the Curie Institute in Paris, France discovered francium in 1939 by purifying a sample of actinium-227, which had been reported to have a decay energy of 220 keV. However, Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one that was separated during purification, but emerged again out of the pure actinium-227. Various tests eliminated the possibility of the unknown element being thorium, radium, lead, bismuth, or thallium. The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, caused by the alpha decay of actinium-227. Perey then attempted to determine the proportion of beta decay to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure that she later revised to 1%.


title: Alkali metal

text: The next element below francium (eka-francium) in the periodic table would be ununennium (Uue), element 119. The synthesis of ununennium was first attempted in 1985 by bombarding a target of einsteinium-254 with calcium-48 ions at the superHILAC accelerator at Berkeley, California. No atoms were identified, leading to a limiting yield of 300 nb.


title: Alkali metal

text: It is highly unlikely that this reaction will be able to create any atoms of ununennium in the near future, given the extremely difficult task of making sufficient amounts of einsteinium-254, which is favoured for production of ultraheavy elements because of its large mass, relatively long half-life of 270 days, and availability in significant amounts of several micrograms, to make a large enough target to increase the sensitivity of the experiment to the required level; einsteinium has not been found in nature and has only been produced in laboratories, and in quantities smaller than those needed for effective synthesis of superheavy elements. However, given that ununennium is only the first period 8 element on the extended periodic table, it may well be discovered in the near future through other reactions, and indeed an attempt to synthesise it is currently ongoing in Japan. Currently, none of the period 8 elements has been discovered yet, and it is also possible, due to drip instabilities, that only the lower period 8 elements, up to around element 128, are physically possible. No attempts at synthesis have been made for any heavier alkali metals: due to their extremely high atomic number, they would require new, more powerful methods and technology to make.


title: Alkali metal

text: The Oddo–Harkins rule holds that elements with even atomic numbers are more common that those with odd atomic numbers, with the exception of hydrogen. This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability. All the alkali metals have odd atomic numbers and they are not as common as the elements with even atomic numbers adjacent to them (the noble gases and the alkaline earth metals) in the Solar System. The heavier alkali metals are also less abundant than the lighter ones as the alkali metals from rubidium onward can only be synthesised in supernovae and not in stellar nucleosynthesis. Lithium is also much less abundant than sodium and potassium as it is poorly synthesised in both Big Bang nucleosynthesis and in stars: the Big Bang could only produce trace quantities of lithium, beryllium and boron due to the absence of a stable nucleus with 5 or 8 nucleons, and stellar nucleosynthesis could only pass this bottleneck by the triple-alpha process, fusing three helium nuclei to form carbon, and skipping over those three elements.


title: Alkali metal

text: The Earth formed from the same cloud of matter that formed the Sun, but the planets acquired different compositions during the formation and evolution of the solar system. In turn, the natural history of the Earth caused parts of this planet to have differing concentrations of the elements. The mass of the Earth is approximately 5.98 kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to planetary differentiation, the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.


title: Alkali metal

text: The alkali metals, due to their high reactivity, do not occur naturally in pure form in nature. They are lithophiles and therefore remain close to the Earth's surface because they combine readily with oxygen and so associate strongly with silica, forming relatively low-density minerals that do not sink down into the Earth's core. Potassium, rubidium and caesium are also incompatible elements due to their large ionic radii.


title: Alkali metal

text: Sodium and potassium are very abundant in earth, both being among the ten most common elements in Earth's crust; sodium makes up approximately 2.6% of the Earth's crust measured by weight, making it the sixth most abundant element overall and the most abundant alkali metal. Potassium makes up approximately 1.5% of the Earth's crust and is the seventh most abundant element. Sodium is found in many different minerals, of which the most common is ordinary salt (sodium chloride), which occurs in vast quantities dissolved in seawater. Other solid deposits include halite, amphibole, cryolite, nitratine, and zeolite. Many of these solid deposits occur as a result of ancient seas evaporating, which still occurs now in places such as Utah's Great Salt Lake and the Dead Sea. Despite their near-equal abundance in Earth's crust, sodium is far more common than potassium in the ocean, both because potassium's larger size makes its salts less soluble, and because potassium is bound by silicates in soil and what potassium leaches is absorbed far more readily by plant life than sodium.


title: Alkali metal

text: Despite its chemical similarity, lithium typically does not occur together with sodium or potassium due to its smaller size. Due to its relatively low reactivity, it can be found in seawater in large amounts; it is estimated that seawater is approximately 0.14 to 0.25 parts per million (ppm) or 25 micromolar. Its diagonal relationship with magnesium often allows it to replace magnesium in ferromagnesium minerals, where its crustal concentration is about 18 ppm, comparable to that of gallium and niobium. Commercially, the most important lithium mineral is spodumene, which occurs in large deposits worldwide.


title: Alkali metal

text: Rubidium is approximately as abundant as zinc and more abundant than copper. It occurs naturally in the minerals leucite, pollucite, carnallite, zinnwaldite, and lepidolite, although none of these contain only rubidium and no other alkali metals. Caesium is more abundant than some commonly known elements, such as antimony, cadmium, tin, and tungsten, but is much less abundant than rubidium.


title: Alkali metal

text: Francium-223, the only naturally occurring isotope of francium, is the product of the alpha decay of actinium-227 and can be found in trace amounts in uranium minerals. In a given sample of uranium, there is estimated to be only one francium atom for every 10 uranium atoms. It has been calculated that there are at most 30 grams of francium in the earth's crust at any time, due to its extremely short half-life of 22 minutes.


title: Alkali metal

text: The physical and chemical properties of the alkali metals can be readily explained by their having an ns valence electron configuration, which results in weak metallic bonding. Hence, all the alkali metals are soft and have low densities, melting and boiling points, as well as heats of sublimation, vaporisation, and dissociation. They all crystallise in the body-centered cubic crystal structure, and have distinctive flame colours because their outer s electron is very easily excited. The ns configuration also results in the alkali metals having very large atomic and ionic radii, as well as very high thermal and electrical conductivity. Their chemistry is dominated by the loss of their lone valence electron in the outermost s-orbital to form the +1 oxidation state, due to the ease of ionising this electron and the very high second ionisation energy. Most of the chemistry has been observed only for the first five members of the group. The chemistry of francium is not well established due to its extreme radioactivity; thus, the presentation of its properties here is limited. What little is known about francium shows that it is very close in behaviour to caesium, as expected. The physical properties of francium are even sketchier because the bulk element has never been observed; hence any data that may be found in the literature are certainly speculative extrapolations.


title: Alkali metal

text: The alkali metals are more similar to each other than the elements in any other group are to each other. Indeed, the similarity is so great that it is quite difficult to separate potassium, rubidium, and caesium, due to their similar ionic radii; lithium and sodium are more distinct. For instance, when moving down the table, all known alkali metals show increasing atomic radius, decreasing electronegativity, increasing reactivity, and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their densities increase when moving down the table, with the exception that potassium is less dense than sodium. One of the very few properties of the alkali metals that does not display a very smooth trend is their reduction potentials: lithium's value is anomalous, being more negative than the others. This is because the Li ion has a very high hydration energy in the gas phase: though the lithium ion disrupts the structure of water significantly, causing a higher change in entropy, this high hydration energy is enough to make the reduction potentials indicate it as being the most electropositive alkali metal, despite the difficulty of ionising it in the gas phase.


title: Alkali metal

text: The stable alkali metals are all silver-coloured metals except for caesium, which has a pale golden tint: it is one of only three metals that are clearly coloured (the other two being copper and gold). Additionally, the heavy alkaline earth metals calcium, strontium, and barium, as well as the divalent lanthanides europium and ytterbium, are pale yellow, though the colour is much less prominent than it is for caesium. Their lustre tarnishes rapidly in air due to oxidation. They all crystallise in the body-centered cubic crystal structure, and have distinctive flame colours because their outer s electron is very easily excited. Indeed, these flame test colours are the most common way of identifying them since all their salts with common ions are soluble.


title: Alkali metal

text: All the alkali metals are highly reactive and are never found in elemental forms in nature. Because of this, they are usually stored in mineral oil or kerosene (paraffin oil). They react aggressively with the halogens to form the alkali metal halides, which are white ionic crystalline compounds that are all soluble in water except lithium fluoride (Li F). The alkali metals also react with water to form strongly alkaline hydroxides and thus should be handled with great care. The heavier alkali metals react more vigorously than the lighter ones; for example, when dropped into water, caesium produces a larger explosion than potassium if the same number of moles of each metal is used. The alkali metals have the lowest first ionisation energies in their respective periods of the periodic table because of their low effective nuclear charge and the ability to attain a noble gas configuration by losing just one electron. Not only do the alkali metals react with water, but also with proton donors like alcohols and phenols, gaseous ammonia, and alkynes, the last demonstrating the phenomenal degree of their reactivity. Their great power as reducing agents makes them very useful in liberating other metals from their oxides or halides.


title: Alkali metal

text: The second ionisation energy of all of the alkali metals is very high as it is in a full shell that is also closer to the nucleus; thus, they almost always lose a single electron, forming cations. The alkalides are an exception: they are unstable compounds which contain alkali metals in a −1 oxidation state, which is very unusual as before the discovery of the alkalides, the alkali metals were not expected to be able to form anions and were thought to be able to appear in salts only as cations. The alkalide anions have filled s-subshells, which gives them enough stability to exist. All the stable alkali metals except lithium are known to be able to form alkalides, and the alkalides have much theoretical interest due to their unusual stoichiometry and low ionisation potentials. Alkalides are chemically similar to the electrides, which are salts with trapped electrons acting as anions. A particularly striking example of an alkalide is "inverse sodium hydride", HNa (both ions being complexed), as opposed to the usual sodium hydride, NaH: it is unstable in isolation, due to its high energy resulting from the displacement of two electrons from hydrogen to sodium, although several derivatives are predicted to be metastable or stable.


title: Alkali metal

text: In aqueous solution, the alkali metal ions form aqua ions of the formula [M(HO)], where "n" is the solvation number. Their coordination numbers and shapes agree well with those expected from their ionic radii. In aqueous solution the water molecules directly attached to the metal ion are said to belong to the first coordination sphere, also known as the first, or primary, solvation shell. The bond between a water molecule and the metal ion is a dative covalent bond, with the oxygen atom donating both electrons to the bond. Each coordinated water molecule may be attached by hydrogen bonds to other water molecules. The latter are said to reside in the second coordination sphere. However, for the alkali metal cations, the second coordination sphere is not well-defined as the +1 charge on the cation is not high enough to polarise the water molecules in the primary solvation shell enough for them to form strong hydrogen bonds with those in the second coordination sphere, producing a more stable entity. The solvation number for Li has been experimentally determined to be 4, forming the tetrahedral [Li(HO)]: while solvation numbers of 3 to 6 have been found for lithium aqua ions, solvation numbers less than 4 may be the result of the formation of contact ion pairs, and the higher solvation numbers may be interpreted in terms of water molecules that approach [Li(HO)] through a face of the tetrahedron, though molecular dynamic simulations may indicate the existence of an octahedral hexaaqua ion. There are also probably six water molecules in the primary solvation sphere of the sodium ion, forming the octahedral [Na(HO)] ion. While it was previously thought that the heavier alkali metals also formed octahedral hexaaqua ions, it has since been found that potassium and rubidium probably form the [K(HO)] and [Rb(HO)] ions, which have the square antiprismatic structure, and that caesium forms the 12-coordinate [Cs(HO)] ion.


title: Alkali metal

text: The chemistry of lithium shows several differences from that of the rest of the group as the small Li cation polarises anions and gives its compounds a more covalent character. Lithium and magnesium have a diagonal relationship due to their similar atomic radii, so that they show some similarities. For example, lithium forms a stable nitride, a property common among all the alkaline earth metals (magnesium's group) but unique among the alkali metals. In addition, among their respective groups, only lithium and magnesium form organometallic compounds with significant covalent character (e.g. LiMe and MgMe).


title: Alkali metal

text: Lithium fluoride is the only alkali metal halide that is poorly soluble in water, and lithium hydroxide is the only alkali metal hydroxide that is not deliquescent. Conversely, lithium perchlorate and other lithium salts with large anions that cannot be polarised are much more stable than the analogous compounds of the other alkali metals, probably because Li has a high solvation energy. This effect also means that most simple lithium salts are commonly encountered in hydrated form, because the anhydrous forms are extremely hygroscopic: this allows salts like lithium chloride and lithium bromide to be used in dehumidifiers and air-conditioners.


title: Alkali metal

text: Francium is also predicted to show some differences due to its high atomic weight, causing its electrons to travel at considerable fractions of the speed of light and thus making relativistic effects more prominent. In contrast to the trend of decreasing electronegativities and ionisation energies of the alkali metals, francium's electronegativity and ionisation energy are predicted to be higher than caesium's due to the relativistic stabilisation of the 7s electrons; also, its atomic radius is expected to be abnormally low. Thus, contrary to expectation, caesium is the most reactive of the alkali metals, not francium. All known physical properties of francium also deviate from the clear trends going from lithium to caesium, such as the first ionisation energy, electron affinity, and anion polarisability, though due to the paucity of known data about francium many sources give extrapolated values, ignoring that relativistic effects make the trend from lithium to caesium become inapplicable at francium. Some of the few properties of francium that have been predicted taking relativity into account are the electron affinity (47.2 kJ/mol) and the enthalpy of dissociation of the Fr molecule (42.1 kJ/mol). The CsFr molecule is polarised as CsFr, showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium. Additionally, francium superoxide (FrO) is expected to have significant covalent character, unlike the other alkali metal superoxides, because of bonding contributions from the 6p electrons of francium.


title: Alkali metal

text: All the alkali metals have odd atomic numbers; hence, their isotopes must be either odd–odd (both proton and neutron number are odd) or odd–even (proton number is odd, but neutron number is even). Odd–odd nuclei have even mass numbers, whereas odd–even nuclei have odd mass numbers. Odd–odd primordial nuclides are rare because most odd–odd nuclei are highly unstable with respect to beta decay, because the decay products are even–even, and are therefore more strongly bound, due to nuclear pairing effects.


title: Alkali metal

text: Due to the great rarity of odd–odd nuclei, almost all the primordial isotopes of the alkali metals are odd–even (the exceptions being the light stable isotope lithium-6 and the long-lived radioisotope potassium-40). For a given odd mass number, there can be only a single beta-stable nuclide, since there is not a difference in binding energy between even–odd and odd–even comparable to that between even–even and odd–odd, leaving other nuclides of the same mass number (isobars) free to beta decay toward the lowest-mass nuclide. An effect of the instability of an odd number of either type of nucleons is that odd-numbered elements, such as the alkali metals, tend to have fewer stable isotopes than even-numbered elements. Of the 26 monoisotopic elements that have only a single stable isotope, all but one have an odd atomic number and all but one also have an even number of neutrons. Beryllium is the single exception to both rules, due to its low atomic number.


title: Alkali metal

text: All of the alkali metals except lithium and caesium have at least one naturally occurring radioisotope: sodium-22 and sodium-24 are trace radioisotopes produced cosmogenically, potassium-40 and rubidium-87 have very long half-lives and thus occur naturally, and all isotopes of francium are radioactive. Caesium was also thought to be radioactive in the early 20th century, although it has no naturally occurring radioisotopes. (Francium had not been discovered yet at that time.) The natural long-lived radioisotope of potassium, potassium-40, makes up about 0.012% of natural potassium, and thus natural potassium is weakly radioactive. This natural radioactivity became a basis for a mistaken claim of the discovery for element 87 (the next alkali metal after caesium) in 1925. Natural rubidium is similarly slightly radioactive, with 27.83% being the long-lived radioisotope rubidium-87.


title: Alkali metal

text: Caesium-137, with a half-life of 30.17 years, is one of the two principal medium-lived fission products, along with strontium-90, which are responsible for most of the radioactivity of spent nuclear fuel after several years of cooling, up to several hundred years after use. It constitutes most of the radioactivity still left from the Chernobyl accident. Caesium-137 undergoes high-energy beta decay and eventually becomes stable barium-137. It is a strong emitter of gamma radiation. Caesium-137 has a very low rate of neutron capture and cannot be feasibly disposed of in this way, but must be allowed to decay. Caesium-137 has been used as a tracer in hydrologic studies, analogous to the use of tritium. Small amounts of caesium-134 and caesium-137 were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Goiânia accident and the Chernobyl disaster. As of 2005, caesium-137 is the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant. Its chemical properties as one of the alkali metals make it one of most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to the high water solubility of its salts, and is taken up by the body, which mistakes it for its essential congeners sodium and potassium.


title: Alkali metal

text: The alkali metals are more similar to each other than the elements in any other group are to each other. For instance, when moving down the table, all known alkali metals show increasing atomic radius, decreasing electronegativity, increasing reactivity, and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their densities increase when moving down the table, with the exception that potassium is less dense than sodium.


title: Alkali metal

text: The atomic radii of the alkali metals increase going down the group. Because of the shielding effect, when an atom has more than one electron shell, each electron feels electric repulsion from the other electrons as well as electric attraction from the nucleus. In the alkali metals, the outermost electron only feels a net charge of +1, as some of the nuclear charge (which is equal to the atomic number) is cancelled by the inner electrons; the number of inner electrons of an alkali metal is always one less than the nuclear charge. Therefore, the only factor which affects the atomic radius of the alkali metals is the number of electron shells. Since this number increases down the group, the atomic radius must also increase down the group.


title: Alkali metal

text: The ionic radii of the alkali metals are much smaller than their atomic radii. This is because the outermost electron of the alkali metals is in a different electron shell than the inner electrons, and thus when it is removed the resulting atom has one fewer electron shell and is smaller. Additionally, the effective nuclear charge has increased, and thus the electrons are attracted more strongly towards the nucleus and the ionic radius decreases.


title: Alkali metal

text: The first ionisation energy of an element or molecule is the energy required to move the most loosely held electron from one mole of gaseous atoms of the element or molecules to form one mole of gaseous ions with electric charge +1. The factors affecting the first ionisation energy are the nuclear charge, the amount of shielding by the inner electrons and the distance from the most loosely held electron from the nucleus, which is always an outer electron in main group elements. The first two factors change the effective nuclear charge the most loosely held electron feels. Since the outermost electron of alkali metals always feels the same effective nuclear charge (+1), the only factor which affects the first ionisation energy is the distance from the outermost electron to the nucleus. Since this distance increases down the group, the outermost electron feels less attraction from the nucleus and thus the first ionisation energy decreases. (This trend is broken in francium due to the relativistic stabilisation and contraction of the 7s orbital, bringing francium's valence electron closer to the nucleus than would be expected from non-relativistic calculations. This makes francium's outermost electron feel more attraction from the nucleus, increasing its first ionisation energy slightly beyond that of caesium.)


title: Alkali metal

text: The second ionisation energy of the alkali metals is much higher than the first as the second-most loosely held electron is part of a fully filled electron shell and is thus difficult to remove.


title: Alkali metal

text: The reactivities of the alkali metals increase going down the group. This is the result of a combination of two factors: the first ionisation energies and atomisation energies of the alkali metals. Because the first ionisation energy of the alkali metals decreases down the group, it is easier for the outermost electron to be removed from the atom and participate in chemical reactions, thus increasing reactivity down the group. The atomisation energy measures the strength of the metallic bond of an element, which falls down the group as the atoms increase in radius and thus the metallic bond must increase in length, making the delocalised electrons further away from the attraction of the nuclei of the heavier alkali metals. Adding the atomisation and first ionisation energies gives a quantity closely related to (but not equal to) the activation energy of the reaction of an alkali metal with another substance. This quantity decreases going down the group, and so does the activation energy; thus, chemical reactions can occur faster and the reactivity increases down the group.


title: Alkali metal

text: Electronegativity is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. If the bond between sodium and chlorine in sodium chloride were covalent, the pair of shared electrons would be attracted to the chlorine because the effective nuclear charge on the outer electrons is +7 in chlorine but is only +1 in sodium. The electron pair is attracted so close to the chlorine atom that they are practically transferred to the chlorine atom (an ionic bond). However, if the sodium atom was replaced by a lithium atom, the electrons will not be attracted as close to the chlorine atom as before because the lithium atom is smaller, making the electron pair more strongly attracted to the closer effective nuclear charge from lithium. Hence, the larger alkali metal atoms (further down the group) will be less electronegative as the bonding pair is less strongly attracted towards them. As mentioned previously, francium is expected to be an exception.


title: Alkali metal

text: Because of the higher electronegativity of lithium, some of its compounds have a more covalent character. For example, lithium iodide (Li I) will dissolve in organic solvents, a property of most covalent compounds. Lithium fluoride (LiF) is the only alkali halide that is not soluble in water, and lithium hydroxide (LiOH) is the only alkali metal hydroxide that is not deliquescent.


title: Alkali metal

text: The melting point of a substance is the point where it changes state from solid to liquid while the boiling point of a substance (in liquid state) is the point where the vapour pressure of the liquid equals the environmental pressure surrounding the liquid and all the liquid changes state to gas. As a metal is heated to its melting point, the metallic bonds keeping the atoms in place weaken so that the atoms can move around, and the metallic bonds eventually break completely at the metal's boiling point. Therefore, the falling melting and boiling points of the alkali metals indicate that the strength of the metallic bonds of the alkali metals decreases down the group. This is because metal atoms are held together by the electromagnetic attraction from the positive ions to the delocalised electrons. As the atoms increase in size going down the group (because their atomic radius increases), the nuclei of the ions move further away from the delocalised electrons and hence the metallic bond becomes weaker so that the metal can more easily melt and boil, thus lowering the melting and boiling points. (The increased nuclear charge is not a relevant factor due to the shielding effect.)


title: Alkali metal

text: The alkali metals all have the same crystal structure (body-centred cubic) and thus the only relevant factors are the number of atoms that can fit into a certain volume and the mass of one of the atoms, since density is defined as mass per unit volume. The first factor depends on the volume of the atom and thus the atomic radius, which increases going down the group; thus, the volume of an alkali metal atom increases going down the group. The mass of an alkali metal atom also increases going down the group. Thus, the trend for the densities of the alkali metals depends on their atomic weights and atomic radii; if figures for these two factors are known, the ratios between the densities of the alkali metals can then be calculated. The resultant trend is that the densities of the alkali metals increase down the table, with an exception at potassium. Due to having the lowest atomic weight and the largest atomic radius of all the elements in their periods, the alkali metals are the least dense metals in the periodic table. Lithium, sodium, and potassium are the only three metals in the periodic table that are less dense than water: in fact, lithium is the least dense known solid at room temperature.


title: Alkali metal

text: The alkali metals form complete series of compounds with all usually encountered anions, which well illustrate group trends. These compounds can be described as involving the alkali metals losing electrons to acceptor species and forming monopositive ions. This description is most accurate for alkali halides and becomes less and less accurate as cationic and anionic charge increase, and as the anion becomes larger and more polarisable. For instance, ionic bonding gives way to metallic bonding along the series NaCl, NaO, NaS, NaP, NaAs, NaSb, NaBi, Na.


title: Alkali metal

text: All the alkali metals react vigorously or explosively with cold water, producing an aqueous solution of a strongly basic alkali metal hydroxide and releasing hydrogen gas. This reaction becomes more vigorous going down the group: lithium reacts steadily with effervescence, but sodium and potassium can ignite, and rubidium and caesium sink in water and generate hydrogen gas so rapidly that shock waves form in the water that may shatter glass containers. When an alkali metal is dropped into water, it produces an explosion, of which there are two separate stages. The metal reacts with the water first, breaking the hydrogen bonds in the water and producing hydrogen gas; this takes place faster for the more reactive heavier alkali metals. Second, the heat generated by the first part of the reaction often ignites the hydrogen gas, causing it to burn explosively into the surrounding air. This secondary hydrogen gas explosion produces the visible flame above the bowl of water, lake or other body of water, not the initial reaction of the metal with water (which tends to happen mostly under water). The alkali metal hydroxides are the most basic known hydroxides.


title: Alkali metal

text: Recent research has suggested that the explosive behavior of alkali metals in water is driven by a Coulomb explosion rather than solely by rapid generation of hydrogen itself. All alkali metals melt as a part of the reaction with water. Water molecules ionise the bare metallic surface of the liquid metal, leaving a positively charged metal surface and negatively charged water ions. The attraction between the charged metal and water ions will rapidly increase the surface area, causing an exponential increase of ionisation. When the repulsive forces within the liquid metal surface exceeds the forces of the surface tension, it vigorously explodes.


title: Alkali metal

text: The hydroxides themselves are the most basic hydroxides known, reacting with acids to give salts and with alcohols to give oligomeric alkoxides. They easily react with carbon dioxide to form carbonates or bicarbonates, or with hydrogen sulfide to form sulfides or bisulfides, and may be used to separate thiols from petroleum. They react with amphoteric oxides: for example, the oxides of aluminium, zinc, tin, and lead react with the alkali metal hydroxides to give aluminates, zincates, stannates, and plumbates. Silicon dioxide is acidic, and thus the alkali metal hydroxides can also attack silicate glass.


title: Alkali metal

text: The alkali metals form many intermetallic compounds with each other and the elements from groups 2 to 13 in the periodic table of varying stoichiometries, such as the sodium amalgams with mercury, including NaHg and NaHg. Some of these have ionic characteristics: taking the alloys with gold, the most electronegative of metals, as an example, NaAu and KAu are metallic, but RbAu and CsAu are semiconductors. NaK is an alloy of sodium and potassium that is very useful because it is liquid at room temperature, although precautions must be taken due to its extreme reactivity towards water and air. The eutectic mixture melts at −12.6 °C. An alloy of 41% caesium, 47% sodium, and 12% potassium has the lowest known melting point of any metal or alloy, −78 °C.


title: Alkali metal

text: The intermetallic compounds of the alkali metals with the heavier group 13 elements (aluminium, gallium, indium, and thallium), such as NaTl, are poor conductors or semiconductors, unlike the normal alloys with the preceding elements, implying that the alkali metal involved has lost an electron to the Zintl anions involved. Nevertheless, while the elements in group 14 and beyond tend to form discrete anionic clusters, group 13 elements tend to form polymeric ions with the alkali metal cations located between the giant ionic lattice. For example, NaTl consists of a polymeric anion (—Tl—) with a covalent diamond cubic structure with Na ions located between the anionic lattice. The larger alkali metals cannot fit similarly into an anionic lattice and tend to force the heavier group 13 elements to form anionic clusters.


title: Alkali metal

text: Boron is a special case, being the only nonmetal in group 13. The alkali metal borides tend to be boron-rich, involving appreciable boron–boron bonding involving deltahedral structures, and are thermally unstable due to the alkali metals having a very high vapour pressure at elevated temperatures. This makes direct synthesis problematic because the alkali metals do not react with boron below 700 °C, and thus this must be accomplished in sealed containers with the alkali metal in excess. Furthermore, exceptionally in this group, reactivity with boron decreases down the group: lithium reacts completely at 700 °C, but sodium at 900 °C and potassium not until 1200 °C, and the reaction is instantaneous for lithium but takes hours for potassium. Rubidium and caesium borides have not even been characterised. Various phases are known, such as LiB, NaB, NaB, and KB. Under high pressure the boron–boron bonding in the lithium borides changes from following Wade's rules to forming Zintl anions like the rest of group 13.


title: Alkali metal

text: Lithium and sodium react with carbon to form acetylides, LiC and NaC, which can also be obtained by reaction of the metal with acetylene. Potassium, rubidium, and caesium react with graphite; their atoms are intercalated between the hexagonal graphite layers, forming graphite intercalation compounds of formulae MC (dark grey, almost black), MC (dark grey, almost black), MC (blue), MC (steel blue), and MC (bronze) (M = K, Rb, or Cs). These compounds are over 200 times more electrically conductive than pure graphite, suggesting that the valence electron of the alkali metal is transferred to the graphite layers (e.g. ). Upon heating of KC, the elimination of potassium atoms results in the conversion in sequence to KC, KC, KC and finally KC. KC is a very strong reducing agent and is pyrophoric and explodes on contact with water. While the larger alkali metals (K, Rb, and Cs) initially form MC, the smaller ones initially form MC, and indeed they require reaction of the metals with graphite at high temperatures around 500 °C to form. Apart from this, the alkali metals are such strong reducing agents that they can even reduce buckminsterfullerene to produce solid fullerides MC; sodium, potassium, rubidium, and caesium can form fullerides where "n" = 2, 3, 4, or 6, and rubidium and caesium additionally can achieve "n" = 1.


title: Alkali metal

text: When the alkali metals react with the heavier elements in the carbon group (silicon, germanium, tin, and lead), ionic substances with cage-like structures are formed, such as the silicides MSi (M = K, Rb, or Cs), which contains M and tetrahedral ions. The chemistry of alkali metal germanides, involving the germanide ion Ge and other cluster (Zintl) ions such as , , , and [(Ge)], is largely analogous to that of the corresponding silicides. Alkali metal stannides are mostly ionic, sometimes with the stannide ion (Sn), and sometimes with more complex Zintl ions such as , which appears in tetrapotassium nonastannide (KSn). The monatomic plumbide ion (Pb) is unknown, and indeed its formation is predicted to be energetically unfavourable; alkali metal plumbides have complex Zintl ions, such as . These alkali metal germanides, stannides, and plumbides may be produced by reducing germanium, tin, and lead with sodium metal in liquid ammonia.


title: Alkali metal

text: Lithium, the lightest of the alkali metals, is the only alkali metal which reacts with nitrogen at standard conditions, and its nitride is the only stable alkali metal nitride. Nitrogen is an unreactive gas because breaking the strong triple bond in the dinitrogen molecule (N) requires a lot of energy. The formation of an alkali metal nitride would consume the ionisation energy of the alkali metal (forming M ions), the energy required to break the triple bond in N and the formation of N ions, and all the energy released from the formation of an alkali metal nitride is from the lattice energy of the alkali metal nitride. The lattice energy is maximised with small, highly charged ions; the alkali metals do not form highly charged ions, only forming ions with a charge of +1, so only lithium, the smallest alkali metal, can release enough lattice energy to make the reaction with nitrogen exothermic, forming lithium nitride. The reactions of the other alkali metals with nitrogen would not release enough lattice energy and would thus be endothermic, so they do not form nitrides at standard conditions. Sodium nitride (NaN) and potassium nitride (KN), while existing, are extremely unstable, being prone to decomposing back into their constituent elements, and cannot be produced by reacting the elements with each other at standard conditions. Steric hindrance forbids the existence of rubidium or caesium nitride. However, sodium and potassium form colourless azide salts involving the linear anion; due to the large size of the alkali metal cations, they are thermally stable enough to be able to melt before decomposing.


title: Alkali metal

text: All the alkali metals react readily with phosphorus and arsenic to form phosphides and arsenides with the formula MPn (where M represents an alkali metal and Pn represents a pnictogen – phosphorus, arsenic, antimony, or bismuth). This is due to the greater size of the P and As ions, so that less lattice energy needs to be released for the salts to form. These are not the only phosphides and arsenides of the alkali metals: for example, potassium has nine different known phosphides, with formulae KP, KP, KP, KP, KP, KP, KP, KP, and KP. While most metals form arsenides, only the alkali and alkaline earth metals form mostly ionic arsenides. The structure of NaAs is complex with unusually short Na–Na distances of 328–330 pm which are shorter than in sodium metal, and this indicates that even with these electropositive metals the bonding cannot be straightforwardly ionic. Other alkali metal arsenides not conforming to the formula MAs are known, such as LiAs, which has a metallic lustre and electrical conductivity indicating the presence of some metallic bonding. The antimonides are unstable and reactive as the Sb ion is a strong reducing agent; reaction of them with acids form the toxic and unstable gas stibine (SbH). Indeed, they have some metallic properties, and the alkali metal antimonides of stoichiometry MSb involve antimony atoms bonded in a spiral Zintl structure. Bismuthides are not even wholly ionic; they are intermetallic compounds containing partially metallic and partially ionic bonds.


title: Alkali metal

text: All the alkali metals react vigorously with oxygen at standard conditions. They form various types of oxides, such as simple oxides (containing the O ion), peroxides (containing the ion, where there is a single bond between the two oxygen atoms), superoxides (containing the ion), and many others. Lithium burns in air to form lithium oxide, but sodium reacts with oxygen to form a mixture of sodium oxide and sodium peroxide. Potassium forms a mixture of potassium peroxide and potassium superoxide, while rubidium and caesium form the superoxide exclusively. Their reactivity increases going down the group: while lithium, sodium and potassium merely burn in air, rubidium and caesium are pyrophoric (spontaneously catch fire in air).


title: Alkali metal

text: The smaller alkali metals tend to polarise the larger anions (the peroxide and superoxide) due to their small size. This attracts the electrons in the more complex anions towards one of its constituent oxygen atoms, forming an oxide ion and an oxygen atom. This causes lithium to form the oxide exclusively on reaction with oxygen at room temperature. This effect becomes drastically weaker for the larger sodium and potassium, allowing them to form the less stable peroxides. Rubidium and caesium, at the bottom of the group, are so large that even the least stable superoxides can form. Because the superoxide releases the most energy when formed, the superoxide is preferentially formed for the larger alkali metals where the more complex anions are not polarised. (The oxides and peroxides for these alkali metals do exist, but do not form upon direct reaction of the metal with oxygen at standard conditions.) In addition, the small size of the Li and O ions contributes to their forming a stable ionic lattice structure. Under controlled conditions, however, all the alkali metals, with the exception of francium, are known to form their oxides, peroxides, and superoxides. The alkali metal peroxides and superoxides are powerful oxidising agents. Sodium peroxide and potassium superoxide react with carbon dioxide to form the alkali metal carbonate and oxygen gas, which allows them to be used in submarine air purifiers; the presence of water vapour, naturally present in breath, makes the removal of carbon dioxide by potassium superoxide even more efficient. All the stable alkali metals except lithium can form red ozonides (MO) through low-temperature reaction of the powdered anhydrous hydroxide with ozone: the ozonides may be then extracted using liquid ammonia. They slowly decompose at standard conditions to the superoxides and oxygen, and hydrolyse immediately to the hydroxides when in contact with water. Potassium, rubidium, and caesium also form sesquioxides MO, which may be better considered peroxide disuperoxides, .


title: Alkali metal

text: Rubidium and caesium can form a great variety of suboxides with the metals in formal oxidation states below +1. Rubidium can form RbO and RbO (copper-coloured) upon oxidation in air, while caesium forms an immense variety of oxides, such as the ozonide CsO and several brightly coloured suboxides, such as CsO (bronze), CsO (red-violet), CsO (violet), CsO (dark green), CsO, CsO, as well as CsO. The last of these may be heated under vacuum to generate CsO.


title: Alkali metal

text: The alkali metals can also react analogously with the heavier chalcogens (sulfur, selenium, tellurium, and polonium), and all the alkali metal chalcogenides are known (with the exception of francium's). Reaction with an excess of the chalcogen can similarly result in lower chalcogenides, with chalcogen ions containing chains of the chalcogen atoms in question. For example, sodium can react with sulfur to form the sulfide (NaS) and various polysulfides with the formula NaS ("x" from 2 to 6), containing the ions. Due to the basicity of the Se and Te ions, the alkali metal selenides and tellurides are alkaline in solution; when reacted directly with selenium and tellurium, alkali metal polyselenides and polytellurides are formed along with the selenides and tellurides with the and ions. They may be obtained directly from the elements in liquid ammonia or when air is not present, and are colourless, water-soluble compounds that air oxidises quickly back to selenium or tellurium. The alkali metal polonides are all ionic compounds containing the Po ion; they are very chemically stable and can be produced by direct reaction of the elements at around 300–400 °C.


title: Alkali metal

text: The alkali metals are among the most electropositive elements on the periodic table and thus tend to bond ionically to the most electronegative elements on the periodic table, the halogens (fluorine, chlorine, bromine, iodine, and astatine), forming salts known as the alkali metal halides. The reaction is very vigorous and can sometimes result in explosions. All twenty stable alkali metal halides are known; the unstable ones are not known, with the exception of sodium astatide, because of the great instability and rarity of astatine and francium. The most well-known of the twenty is certainly sodium chloride, otherwise known as common salt. All of the stable alkali metal halides have the formula MX where M is an alkali metal and X is a halogen. They are all white ionic crystalline solids that have high melting points. All the alkali metal halides are soluble in water except for lithium fluoride (LiF), which is insoluble in water due to its very high lattice enthalpy. The high lattice enthalpy of lithium fluoride is due to the small sizes of the Li and F ions, causing the electrostatic interactions between them to be strong: a similar effect occurs for magnesium fluoride, consistent with the diagonal relationship between lithium and magnesium.


title: Alkali metal

text: The alkali metals also react similarly with hydrogen to form ionic alkali metal hydrides, where the hydride anion acts as a pseudohalide: these are often used as reducing agents, producing hydrides, complex metal hydrides, or hydrogen gas. Other pseudohalides are also known, notably the cyanides. These are isostructural to the respective halides except for lithium cyanide, indicating that the cyanide ions may rotate freely. Ternary alkali metal halide oxides, such as NaClO, KBrO (yellow), NaBrO, NaIO, and KBrO, are also known. The polyhalides are rather unstable, although those of rubidium and caesium are greatly stabilised by the feeble polarising power of these extremely large cations.


title: Alkali metal

text: Alkali metal cations do not usually form coordination complexes with simple Lewis bases due to their low charge of just +1 and their relatively large size; thus the Li ion forms most complexes and the heavier alkali metal ions form less and less (though exceptions occur for weak complexes). Lithium in particular has a very rich coordination chemistry in which it exhibits coordination numbers from 1 to 12, although octahedral hexacoordination is its preferred mode. In aqueous solution, the alkali metal ions exist as octahedral hexahydrate complexes ([M(HO))]), with the exception of the lithium ion, which due to its small size forms tetrahedral tetrahydrate complexes ([Li(HO))]); the alkali metals form these complexes because their ions are attracted by electrostatic forces of attraction to the polar water molecules. Because of this, anhydrous salts containing alkali metal cations are often used as desiccants. Alkali metals also readily form complexes with crown ethers (e.g. 12-crown-4 for Li, 15-crown-5 for Na, 18-crown-6 for K, and 21-crown-7 for Rb) and cryptands due to electrostatic attraction.


title: Alkali metal

text: The alkali metals dissolve slowly in liquid ammonia, forming ammoniacal solutions of solvated metal cation M and solvated electron e, which react to form hydrogen gas and the alkali metal amide (MNH, where M represents an alkali metal): this was first noted by Humphry Davy in 1809 and rediscovered by W. Weyl in 1864. The process may be speeded up by a catalyst. Similar solutions are formed by the heavy divalent alkaline earth metals calcium, strontium, barium, as well as the divalent lanthanides, europium and ytterbium. The amide salt is quite insoluble and readily precipitates out of solution, leaving intensely coloured ammonia solutions of the alkali metals. In 1907, Charles Krause identified the colour as being due to the presence of solvated electrons, which contribute to the high electrical conductivity of these solutions. At low concentrations (below 3 M), the solution is dark blue and has ten times the conductivity of aqueous sodium chloride; at higher concentrations (above 3 M), the solution is copper-coloured and has approximately the conductivity of liquid metals like mercury. In addition to the alkali metal amide salt and solvated electrons, such ammonia solutions also contain the alkali metal cation (M), the neutral alkali metal atom (M), diatomic alkali metal molecules (M) and alkali metal anions (M). These are unstable and eventually become the more thermodynamically stable alkali metal amide and hydrogen gas. Solvated electrons are powerful reducing agents and are often used in chemical synthesis.


title: Alkali metal

text: Being the smallest alkali metal, lithium forms the widest variety of and most stable organometallic compounds, which are bonded covalently. Organolithium compounds are electrically non-conducting volatile solids or liquids that melt at low temperatures, and tend to form oligomers with the structure (RLi) where R is the organic group. As the electropositive nature of lithium puts most of the charge density of the bond on the carbon atom, effectively creating a carbanion, organolithium compounds are extremely powerful bases and nucleophiles. For use as bases, butyllithiums are often used and are commercially available. An example of an organolithium compound is methyllithium ((CHLi)), which exists in tetrameric ("x" = 4, tetrahedral) and hexameric ("x" = 6, octahedral) forms. Organolithium compounds, especially "n"-butyllithium, are useful reagents in organic synthesis, as might be expected given lithium's diagonal relationship with magnesium, which plays an important role in the Grignard reaction. For example, alkyllithiums and aryllithiums may be used to synthesise aldehydes and ketones by reaction with metal carbonyls. The reaction with nickel tetracarbonyl, for example, proceeds through an unstable acyl nickel carbonyl complex which then undergoes electrophilic substitution to give the desired aldehyde (using H as the electrophile) or ketone (using an alkyl halide) product.


title: Alkali metal

text: Alkyllithiums and aryllithiums may also react with "N","N"-disubstituted amides to give aldehydes and ketones, and symmetrical ketones by reacting with carbon monoxide. They thermally decompose to eliminate a β-hydrogen, producing alkenes and lithium hydride: another route is the reaction of ethers with alkyl- and aryllithiums that act as strong bases. In non-polar solvents, aryllithiums react as the carbanions they effectively are, turning carbon dioxide to aromatic carboxylic acids (ArCOH) and aryl ketones to tertiary carbinols (Ar'C(Ar)OH). Finally, they may be used to synthesise other organometallic compounds through metal-halogen exchange.


title: Alkali metal

text: Unlike the organolithium compounds, the organometallic compounds of the heavier alkali metals are predominantly ionic. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are commercially available and exhibit more convenient reactivity. The principal organosodium compound of commercial importance is sodium cyclopentadienide. Sodium tetraphenylborate can also be classified as an organosodium compound since in the solid state sodium is bound to the aryl groups. Organometallic compounds of the higher alkali metals are even more reactive than organosodium compounds and of limited utility. A notable reagent is Schlosser's base, a mixture of "n"-butyllithium and potassium "tert"-butoxide. This reagent reacts with propene to form the compound allylpotassium (KCHCHCH). "cis"-2-Butene and "trans"-2-butene equilibrate when in contact with alkali metals. Whereas isomerisation is fast with lithium and sodium, it is slow with the heavier alkali metals. The heavier alkali metals also favour the sterically congested conformation. Several crystal structures of organopotassium compounds have been reported, establishing that they, like the sodium compounds, are polymeric. Organosodium, organopotassium, organorubidium and organocaesium compounds are all mostly ionic and are insoluble (or nearly so) in nonpolar solvents.


title: Alkali metal

text: Alkyl and aryl derivatives of sodium and potassium tend to react with air. They cause the cleavage of ethers, generating alkoxides. Unlike alkyllithium compounds, alkylsodiums and alkylpotassiums cannot be made by reacting the metals with alkyl halides because Wurtz coupling occurs:


title: Alkali metal

text: As such, they have to be made by reacting alkylmercury compounds with sodium or potassium metal in inert hydrocarbon solvents. While methylsodium forms tetramers like methyllithium, methylpotassium is more ionic and has the nickel arsenide structure with discrete methyl anions and potassium cations.


title: Alkali metal

text: The alkali metals and their hydrides react with acidic hydrocarbons, for example cyclopentadienes and terminal alkynes, to give salts. Liquid ammonia, ether, or hydrocarbon solvents are used, the most common of which being tetrahydrofuran. The most important of these compounds is sodium cyclopentadienide, NaCH, an important precursor to many transition metal cyclopentadienyl derivatives. Similarly, the alkali metals react with cyclooctatetraene in tetrahydrofuran to give alkali metal cyclooctatetraenides; for example, dipotassium cyclooctatetraenide (KCH) is an important precursor to many metal cyclooctatetraenyl derivatives, such as uranocene. The large and very weakly polarising alkali metal cations can stabilise large, aromatic, polarisable radical anions, such as the dark-green sodium naphthalenide, Na[CH•], a strong reducing agent.


title: Alkali metal

text: Upon reacting with oxygen, alkali metals form oxides, peroxides, superoxides and suboxides. However, the first three are more common. The table below shows the types of compounds formed in reaction with oxygen. The compound in brackets represents the minor product of combustion.


title: Alkali metal

text: The alkali metal peroxides are ionic compounds that are unstable in water. The peroxide anion is weakly bound to the cation, and it is hydrolysed, forming stronger covalent bonds.


title: Alkali metal

text: Because alkali metal sulfides are essentially salts of a weak acid and a strong base, they form basic solutions.


title: Alkali metal

text: Lithium is the only metal that reacts directly with carbon to give dilithium acetylide. Na and K can react with acetylene to give acetylides.


title: Alkali metal

text: On reaction with water, they generate hydroxide ions and hydrogen gas. This reaction is vigorous and highly exothermic and the hydrogen resulted may ignite in air or even explode in the case of Rb and Cs.


title: Alkali metal

text: The alkali metals are very good reducing agents. They can reduce metal cations that are less electropositive. Titanium is produced industrially by the reduction of titanium tetrachloride with Na at 400C (van Arkel–de Boer process).


title: Alkali metal

text: Alkali metals dissolve in liquid ammonia or other donor solvents like aliphatic amines or hexamethylphosphoramide to give blue solutions. These solutions are believed to contain free electrons.


title: Alkali metal

text: Due to the presence of solvated electrons, these solutions are very powerful reducing agents used in organic synthesis.


title: Alkali metal

text: Although francium is the heaviest alkali metal that has been discovered, there has been some theoretical work predicting the physical and chemical characteristics of hypothetical heavier alkali metals. Being the first period 8 element, the undiscovered element ununennium (element 119) is predicted to be the next alkali metal after francium and behave much like their lighter congeners; however, it is also predicted to differ from the lighter alkali metals in some properties. Its chemistry is predicted to be closer to that of potassium or rubidium instead of caesium or francium. This is unusual as periodic trends, ignoring relativistic effects would predict ununennium to be even more reactive than caesium and francium. This lowered reactivity is due to the relativistic stabilisation of ununennium's valence electron, increasing ununennium's first ionisation energy and decreasing the metallic and ionic radii; this effect is already seen for francium. This assumes that ununennium will behave chemically as an alkali metal, which, although likely, may not be true due to relativistic effects. The relativistic stabilisation of the 8s orbital also increases ununennium's electron affinity far beyond that of caesium and francium; indeed, ununennium is expected to have an electron affinity higher than all the alkali metals lighter than it. Relativistic effects also cause a very large drop in the polarisability of ununennium. On the other hand, ununennium is predicted to continue the trend of melting points decreasing going down the group, being expected to have a melting point between 0 °C and 30 °C.