Llthium (3)

Lithium is a Group 1 (IA) element containing just a single valence electron (1s22s1). Group 1 elements are called "alkali metals". Lithium is a solid only about half as dense as water and lithium metal is the least dense metal. A freshly cut chunk of lithium is silvery, but tarnishes in a minute or so in air to give a grey surface. Its chemistry is dominated by its tendency to lose an electron to ...form Li+. It is the first element within the second period.

Lithium is mixed (alloyed) with aluminium and magnesium for light-weight alloys, and is also used in batteries, some greases, some glasses, and in medicine.

Lithium does not occur as the free metal in nature because of its high reactivity. Deposits are known all around the world. It is a minor component of nearly all igneous rocks and is a component of many natural brines.

•Name: Lithium
•Symbol: Li
•Atomic number: 3
•Atomic weight: [6.941]
•Standard state: solid at 298 K
•CAS Registry ID: 7439-93-2
•Group in periodic table: 1
•Group name: Alkali metal
•Period in periodic table: 2
•Block in periodic table: s-block
•Color: silvery white/grey
•Classification: Metallic

Historical information

Lithium was discovered by Johan August Arfvedson at 1817 in Stockholm, Sweden. Origin of name: from the Greek word "lithos" meaning "stone", apparently because it was discovered from a mineral source whereas the other two common Group 1 elements, sodium and potassium, were discovered from plant sources. The mineral petalite (which contains lithium) was discovered by the Brazilian scientist José Bonifácio de Andrada e Silva towards the end of the 18th century while visiting Sweden. Lithium was discovered by Johan August Arfvedson in 1817 during an analysis of petalite ore, an ore now recognized to be LiAl(Si2O5)2, taken from the Swedish island of Utö. Arfvedson subsequently discovered lithium in the minerals spodumene and lepidolite. C.G. Gmelin observed in 1818 that lithium salts color flames bright red. Neither Gmelin nor Arfvedson were able to isolate the element itself from lithium salts, for example in attempted reductions by heating the oxide with iron or carbon.

The first isolation of elemental lithium was achieved later by W.T. Brande and Sir Humphrey Davy by the electrolysis of lithium oxide. In 1855, Bunsen and Mattiessen isolated larger quantities of the metal by electrolysis of lithium chloride.

In 1923 the first commercial production of lithium metal was achieved by Metallgesellschaft AG in Germany using the electrolysis of a molten mixture of lithium chloride and potassium chloride, exploiting a suggestion made by Guntz in 1893.

Physical properties

•Melting point: 453.69 [or 180.54 °C (356.97 °F)] K
•Boiling point: 1615 [or 1342 °C (2448 °F)] K
•Density of solid: 535 kg m-3

Orbital properties

•Ground state electron configuration: [He].2s1
•Shell structure: 2.1
•Term symbol: 2S1/2
•Pauling electronegativity: 0.98 (Pauling units)

Isolation

Lithium would not normally be made in the laboratory as it is so readily available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative lithium ion Li+.

The ore spodumene, LiAl(SiO3)2, is the most important commercial ore containing lithium. The α form is first converted into the softer β form by heating to around 1100°C. This is mixed carefully with hot sulphuric acid and extracted into water to form lithium sulphate, Li2SO4, solution. The sulphate is washed with sodium carbonate, Na2CO3, to form a precipitate of the relatively insoluble lithium carbonate, Li2CO3.

Li2SO4 + Na2CO3 → Na2SO4 + Li2CO3 (solid)

Reaction of lithium carbonate with HCl then provides lithium chloride, LiCl.

Li2CO3 + 2HCl → 2LiCl + CO2 +H2O

Lithium chloride has a high melting point (> 600°C) meaning that it sould be expensive to melt it in order to carry out the electrolysis. However a mixture of LiCl (55%) and KCl (45%) melts at about 430°C and so much less energy and so expense is required for the electrolysis.

Cathode: Li+(l) + e- → Li (l)                                          Anode: Cl-(l) → 1/2Cl2 (g) + e-