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Last updated on April 18, 2014 at 21:21 EDT

Lithium

Lithium is the chemical element with symbol Li and atomic number 3. In the periodic table, it is located in group 1, among the alkali metals. Lithium in its pure form is a soft, silver white metal, that tarnishes and oxidizes very rapidly in air and water. It is the lightest solid element and is primarily used in heat transfer alloys, in batteries and serves as a component in some drugs known as mood stabilizers.

Notable characteristics

Lithium is the lightest metal and has a density that is only half that of water. Like all alkali metals, lithium reacts easily in water and does not occur freely in nature due to its activity, nevertheless it is still less reactive than the chemically similar sodium. When placed over a flame, this metal gives off a striking crimson color but when it burns strongly, the flame becomes a brilliant white. Lithium is a univalent element.

Applications

Because of its large specific heat (the largest of any solid), lithium is used in heat transfer applications. It is also an important battery anode material due to its high electrochemical potential. Other uses:

- Lithium salts such as lithium carbonate (Li2CO3), lithium citrate, and lithium orotate are mood stabilizers used in the treatment of bipolar disorder, since unlike most other mood altering drugs, they counteract both mania and depression. Lithium can also be used to augment other antidepressant drugs. Useful amounts of Lithium for this use are only slightly lower than toxic amounts, so that the blood levels of Lithium have to be carefully monitored during such a treatment.
- Lithium chloride and lithium bromide are extremely hygroscopic and frequently used as desiccants.
- Lithium stearate is a common all-purpose high-temperature lubricant.
- Lithium is an alloying agent used to synthesize organic compounds, and also has nuclear applications.
- Lithium is sometimes used in glasses and ceramics including the glass for the 200-inch (5.08 m) telescope at Mt. Palomar.
- Lithium hydroxide is employed to extract carbon dioxide from the air in spacecraft and submarines.
- Alloys of the metal with aluminium, cadmium, copper, and manganese are used to make high performance aircraft parts.
- Lithium niobate is used extensively in the telecoms market, such as mobile phones and optical modulators.
- The high non-linearity of lithium niobate also makes a good choice for non-linear applications.
- Lithium hydride (using deuterium instead of hydrogen, and sometimes called lithium deuteride instead of hydride) is used in the making of a hydrogen bomb. When bombarded by neutrons from a fission bomb, lithium deuteride produces copious quantities of tritium. The tritium then participates in the thermonuclear reaction which gives a hydrogen bomb its power.

History

Lithium (Greek lithos, meaning “stone”) was discovered by Johann Arfvedson in 1817. Arfvedson found the new element within the minerals spodumene and lepidolite in a petalite ore, LiAl(Si2O5)2, he was analyzing from the island Utö in Sweden. In 1818 Christian Gmelin was the first to observe that lithium salts give a bright red color in flame. Both men tried and failed to isolate the element from its salts, however.

The element was not isolated until William Thomas Brande and Sir Humphrey Davy later used electrolysis on lithium oxide. Commercial production of lithium metal was achieved in 1923 by the German company Metallgesellschaft AG through using electrolysis of molten lithium chloride and potassium chloride.

It was apparently given the name “lithium” because it was discovered from a mineral while other common alkali metals were first discovered from plant tissue.

Occurrence

Lithium is widely distributed but does not occur in nature in its free form. Because of its reactivity, it is always found bound with one or more other elements or compounds. It forms a minor part of almost all igneous rocks and is also found in many natural brines.

Since the end of World War II, lithium production has greatly increased. 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 Chile. The metal, which is silvery in appearance like sodium, potassium and other members of the alkali metal series, is produced electrolytically from a mixture of fused lithium and potassium chloride. This metal cost about US$ 300 per pound ($650/kg) in 1997.

Isotopes

Naturally occurring lithium is composed of 2 stable isotopes Li-6 and Li-7 with Li-7 being the most abundant (92.5% natural abundance). Seven radioisotopes have been characterized with the most stable being Li-8 with a half-life of 838 ms and Li-9 with a half-life of 178.3 ms. All of the remaining radioactive isotopes have half-lifes 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 7.58043×10-23 s.

Lithium-7 is one of the primordial elements (produced in Big Bang nucleosynthesis). Lithium isotopes fractionate substantially during a wide variety of natural processes, including mineral formation (chemical precipitation), metabolism, ion exchange (Li substitutes for magnesium and iron in octahedral sites in clay minerals, where Li-6 is preferential over Li-7), hyperfiltration, and rock alteration.

Precautions

Like the other alkali metals, lithium in its pure form is highly flammable and slightly explosive when exposed to air and especially water. Lithium metal is also corrosive and requires special handling to avoid skin contact. Lithium should be stored in a non-reactive compound such as naptha or a hydrocarbon. Lithium compounds play no natural biological role and are considered to be slightly toxic. When used as a drug, blood concentrations of Li+ must be carefully monitored.

Lithium