- This article is about the chemical element lithium.
|Name, Symbol, Number||lithium, Li, 3|
|Chemical series||alkali metals|
|Group, Period, Block||1, 2, s|
|Atomic mass||6.941(2) g/mol|
|Electron configuration||1s2 2s1|
|Electrons per shell||2, 1|
|Density (near r.t.)||0.534 g/cm³|
|Liquid density at m.p.||0.512 g/cm³|
|Melting point||453.69 K
(180.54 °C, 356.97 °F)
|Boiling point||1615 K
(1342 °C, 2448 °F)
3223 K, 67 MPa
|Heat of fusion||3.00 kJ/mol|
|Heat of vaporization||147.1 kJ/mol|
|Heat capacity||(25 °C) 24.860 J/(mol·K)|
|Crystal structure||cubic body centered|
(strongly basic oxide)
|Electronegativity||0.98 (Pauling scale)|
|Ionization energies||1st: 520.2 kJ/mol|
|2nd: 7298.1 kJ/mol|
|3rd: 11815.0 kJ/mol|
|Atomic radius||145 pm|
|Atomic radius (calc.)||167 pm|
|Covalent radius||134 pm|
|Van der Waals radius||182 pm|
|Electrical resistivity||(20 °C) 92.8 nΩ·m|
|Thermal conductivity||(300 K) 84.8 W/(m·K)|
|Thermal expansion||(25 °C) 46 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 6000 m/s|
|Speed of sound (thin rod)||(r.t.) 4.9 m/s|
|Shear modulus||4.2 GPa|
|Bulk modulus||11 GPa|
|CAS registry number||7439-93-2|
Lithium (chemical symbol Li, atomic number 3) is the lightest solid chemical element and a member of the group of elements known as alkali metals. It is flammable, corrosive to the skin, and readily reacts with water and air. Pure lithium is soft and silvery white in color, but it tarnishes rapidly. It is one of only four elements theorized to have been created in the first three minutes of the origin of the universe, through a process called "Big Bang nucleosynthesis."
Lithium, its alloys, and compounds have a wide range of applications. For instance, lithium is used in specialized rechargeable batteries, alloys for aircraft parts, and appliances like toasters and microwave ovens. Lithium niobate is used in mobile phones, lithium stearate is a high-temperature lubricant, lithium hydroxide is an efficient air purifier, and lithium chloride and bromide are used as desiccants. In addition, lithium salts are used in mood-stabilizing drugs.
Discovery and etymology
Toward the end of the 1700s, Brazilian scientist José Bonifácio de Andrada e Silva discovered the lithium-containing mineral petalite (LiAl(Si2O5)2) on a trip to Sweden. When Johan Arfvedson analyzed a petalite ore in 1817, he discovered lithium. In 1818, Christian Gmelin was the first to observe that lithium salts give a bright red color when held in a flame. Both Arfvedson and Gmelin tried to isolate the element from its salts but failed.
The element was not isolated until William Thomas Brande and Sir Humphry Davy later performed electrolysis on lithium oxide in 1818. Robert Bunsen and Matiessen isolated larger quantities of the metal by electrolysis of lithium chloride in 1855. Commercial production of lithium metal was achieved in 1923 by a German company (Metallgesellschaft), by the electrolysis of molten lithium chloride and potassium chloride.
The name "lithium" (from the Greek λιθoς (lithos), meaning "stone") was chosen apparently because it was discovered from a mineral, while other common alkali metals were first discovered from plant tissue.
Occurrence and production
The Earth's crust contains about 65 parts per million (ppm) of lithium. The element is widely distributed in nature, but because of its reactivity, it is always found combined with other elements.
Lithium production has greatly increased since the end of World War II. The metal is separated from other elements in igneous rocks, and is also extracted from the water of mineral springs. Lepidolite, spodumene, petalite, and amblygonite are the more important minerals containing it.
In the United States, lithium is recovered from brine pools in Nevada. Today, most commercial lithium is recovered from brine sources in Argentina and Chile. The metal is produced by electrolysis from a mixture of fused (molten) lithium chloride and potassium chloride. Chile is currently the world's leading producer of pure lithium metal.
Lithium leads the family of elements known as "alkali metals" in group 1 of the periodic table. Two well-known elements in this group are sodium and potassium. Lithium is also at the start of period 2, located just before beryllium. The atomic number of lithium is 3, which places it right after helium (atomic number 2). Thus lithium is the lightest metallic element.
Like all other alkali metals, lithium has a single electron in its outermost shell, and it can readily lose this electron to become a positive ion. For this reason, lithium readily reacts with water and does not occur freely in nature. Nevertheless, it is less reactive than the chemically similar sodium.
Lithium is soft enough to be cut with a knife, though this is significantly more difficult to do than cutting sodium. The fresh metal has a silvery color, but it rapidly tarnishes to black in the air. Lithium has only about half the density of water, because of which sticks of this metal have the odd heft of a light wood such as balsa.
In its pure form, lithium is highly flammable and slightly explosive when exposed to water and air. It is the only metal that reacts with nitrogen at room temperature. Lithium fires are difficult to extinguish, requiring special chemicals designed to smother them. For these reasons, storage of lithium in the laboratory involves placing sticks of the metal in jars of nonreactive, liquid hydrocarbons. Given their low density, the sticks tend to float, so they need to be held down mechanically by the lid of the jar and other sticks.
When placed over a flame, lithium gives off a striking crimson color, but when it burns strongly, the flame becomes brilliant white. Lithium has a high specific heat capacity (3582 J/(kg·K)), which means that a large amount of heat is required to raise the temperature of a unit mass (1 kilogram or 1 gram) of the substance by 1 kelvin. In addition, its liquid form has a great temperature range. These properties make lithium a useful chemical.
In humans, lithium compounds play no natural biological role and are considered slightly toxic. The metal is corrosive to the touch and requires special handling to avoid skin contact. By contrast, lithium (in the ionic form) appears to be an essential trace element for goats and possibly rats. When used as a drug, blood concentrations of Li+ must be carefully monitored.
Naturally occurring lithium is composed of 2 stable isotopes, 6Li and 7Li, of which the latter is the more abundant (92.5% natural abundance). In addition, seven radioisotopes have been characterized. Among them, 8Li has a half-life of 838 milliseconds (ms), 9Li has a half-life of 178.3 ms, and the others have half-lives that are less than 8.6 ms. The shortest-lived isotope of lithium is 4Li, which decays through proton emission and has a half-life of 7.58043x10-23 seconds.
According to the "Big Bang" model of the origin of the universe, the nuclei of 7Li were among the few types of atomic nuclei formed shortly after the Big Bang, during a phase called the "Big Bang nucleosynthesis" ("nucleosynthesis" refers to the synthesis of atomic nuclei). It is thought that the nuclei of hydrogen, helium, and beryllium atoms were also formed at that time.
Given that the specific heat capacity of lithium is higher than that of any other solid, lithium is used in heat-transfer applications, such as in toasters and microwave ovens. It is also an important material in rechargeable lithium ion batteries. Besides being lighter than the standard dry cells, these batteries produce a higher voltage (3 volts versus 1.5 volts). Additional uses of lithium, its alloys, and its compounds are as follows:
- Manufacture of materials, parts, and commercial products
- Alloys of lithium with aluminum, cadmium, copper, and manganese are used to make high-performance aircraft parts.
- Lithium is used as a flux to promote the fusing of metals during welding and soldering. It also eliminates the formation of oxides during welding by absorbing impurities. This fusing quality is also important as a flux for producing ceramics, enamels, and glass.
- Lithium niobate is used extensively in telecommunication products, such as mobile phones and optical modulators.
- Lithium stearate is a common, all-purpose, high-temperature lubricant.
- Lithium hydroxide (LiOH) is a strong base that, when heated with a fat, produces a lithium soap. This soap has the ability to thicken oils and is used commercially to manufacture lubricating greases.
- Chemical uses
- Some lithium compounds, such as lithium aluminum hydride (LiAlH4), are used to synthesize organic compounds.
- Lithium chloride and lithium bromide are extremely hygroscopic (that is, they readily absorb moisture) and are frequently used as desiccants.
- Lithium salts such as lithium carbonate, lithium citrate, and lithium orotate are mood stabilizers used in the treatment of bipolar disorder (manic depression). Unlike most other mood-altering drugs, they counteract both mania and depression. The active principle in these salts is the lithium ion (Li+), which interacts with the normal functioning of the sodium ion (Na+) to produce numerous changes in neurotransmitter activity in the brain.
- Lithium can also be used to augment other antidepressant drugs. For these treatments, useful amounts of lithium are only slightly lower than toxic levels, so the blood levels of lithium must be carefully monitored during such use.
- Nuclear reactions
- Lithium is used as a source for alpha particles, or helium nuclei. When 7Li is bombarded by accelerated protons, an isotope of beryllium (8Be) is formed, which undergoes spontaneous fission to form two alpha particles. This was the first manmade nuclear reaction, produced by Cockroft and Walton in 1929.
- Lithium deuteride was the nuclear fusion fuel of choice in early versions of the hydrogen bomb. When bombarded by neutrons, both 6Li and 7Li produce tritium (an isotope of hydrogen). Tritium fuses with deuterium (another isotope of hydrogen) in a nuclear fusion reaction that is relatively easy to achieve. Although details remain secret, lithium apparently no longer plays a role in modern nuclear weapons, having been replaced entirely for this purpose by elemental tritium, which is lighter and easier to handle than lithium salts.
- Lithium hydroxide is an efficient and lightweight air purifier. In confined areas, such as in spacecraft and submarines, carbon dioxide concentrations can approach unhealthy or toxic levels. Lithium hydroxide absorbs the carbon dioxide from the air by reacting with it to form lithium carbonate. (Any alkali hydroxide will absorb CO2, but lithium hydroxide is preferred because of its low atomic weight.) Even better materials for this purpose include lithium peroxide (Li2O2) and lithium superoxide (LiO2) because, in the presence of moisture, they not only absorb carbon dioxide to form lithium carbonate but they also release oxygen.
- Lithium metal is used as a catalyst in some types of methamphetamine production, particularly in illegal amateur "meth labs."
Trends in consumption and production
Consumption of lithium increased by 4-5 percent per year between 2002 and 2005, driven by the demand in lithium secondary batteries. Batteries accounted for 20 percent of total consumption in 2005, a rise from under 10 percent in 2000.
Continued expansion in the portable electronic products market and commercialization of hybrid electric vehicles using lithium batteries suggest growth of up to 10 percent per year in lithium carbonate consumption in this market through 2010.
Between 2002 and 2005, lithium minerals production rose by 7 percent per year to reach 18,800 tons lithium. Chile and Australia account for over 60 percent of total output. China may emerge as a significant producer of brine-based lithium carbonate by 2010. Potential capacity of up to 45,000 tons per year could come on-stream if projects in Qinghai province and Tibet proceed .
Some jurisdictions limit the sale of lithium batteries, which are the most readily available source of lithium metal for regular consumers. Lithium can be used to reduce pseudoephedrine and ephedrine to methamphetamine by the Birch reduction method, which employs alkali metals dissolved in ammonia. The effectiveness of such restrictions in controlling the illegal production of methamphetamine remains indeterminate and controversial.
Carriage and shipment of some types of lithium batteries may be prohibited aboard aircraft, because most types of lithium batteries can discharge very rapidly when short-circuited, leading to overheating and possible explosion. Most consumer lithium batteries, however, have built-in thermal overload protection to prevent this type of incident, or their design limits short-circuit currents.
- Krebs, Robert E. The History and Use of Our Earth's Chemical Elements : A Reference Guide. Westport, Conn.: Greenwood Press, 1998). ISBN 0313301239.
- Newton, David E. The Chemical Elements New York: Franklin Watts, 1994. ISBN 0531125017.
- Stwertka, Albert. A Guide to the Elements. New York: Oxford University Press, 2002. ISBN 0195150279.
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