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| Lithium |
- Atomic number : 3
- Atomic Weight: 6.938
- Electronic configuration: 2, 1
- Density : 0.634 g.cm-3
- Melting point : ( 180oC )
- Boiling point : (1326 oC )
- Flame color : crimson red
Characteristics:
- Lithium is a silvery-white metal.
- It is the lightest metal known.
- Its density is 0.634 g.cm-3.
- It is harder than sodium and potassium but is soft enough to be cut with a knife.
- It is highly reactive and flammable, so it is kept in mineral oil.
- It does not occur freely in nature .
- Main source of lithium is pegmatitic mineral.
- Due to solubility as an ion, it is present in ocean water and is obtained from brine.
- Its has higher melting point ( 180oC ) and higher boiling point ( 1326 oC ) than rest of other alkalis metal.
- Its flame colour is crimson red.
Extraction of Lithium:
- Lithium is fairly widely distributed in nature and is about twice as plentiful as lead. However, the amount present in any mineral is always small and the extraction is not so easy. The important lithium-bearing minerals are:
- Lepidolite or lithia mica (Li,Na,K)2.Al2(SiO3) 3.( F, OH)2 containing up to 1.5% of lithium.
- Petalite, LiAl(Si2O5)4, containing 2.7 to 3.7 % of lithium.
- Spodumene, LiAI(SiO3)2 containing 4 to 6% of lithium.
- Triphylite, (Li, Na)3PO4 .(Fe,Mn)3(PO4)2 containing up to 4% of lithium.
- Lithium salts also occur in certain spring waters and in some plants such as tobacco, beet and sugar-cane.
Lithium uses :
- It is used In the manufacture of various alloy which are highly useful in industry.For example: lithium –lead alloy ( 0.05 % Li ) is used for making bearing and sheaths for electric cables.
- Lithium –Aluminium alloy possesses great tensile strength and elasticity like that of mild steel.
- It is used to refine copper and nickel. Since lithium combine readily with oxygen and nitrogen, so it is used for removing the last traces of oxygen and nitrogen from copper and nickel.
Uses of lithium compounds.
- Lithium carbonate is used in making a special variety of glass which is very strong and resists weather.
- Lithium chloride is used in air-conditioning plants to regulate the humidity. It is also used in Ni-Fe accumulators.
- Lithium salicylate and bicarbonate have been used in medicine for the treatment of rheumatism since the resulting lithium urate is highly soluble.
- Lithium bromide is used in medicine as a sedative.
- Lithium hydride and lithium aluminium hydride (LiAlIH) are used in synthetic organic chemistry as reducing agents.
Comparison of Lithium with Other Members of
the Family:
- Lithium, no doubt, has most of the characteristic properties of the metals of Group -I but it differs from them in many respects. This is mainly due to the small size of the Li atom and the Li+ ion. The small size of Li+ ion is responsible for the highest polarizing power of this ion among all the alkali metal ions. Lithium differs from the other alkali metals in the following respects.
- Lithium is much harder than the rest of the alkali metals. Its melting and boiling points are also higher.
- Lithium is the least reactive of the alkali metals towards the various chemical reagents except hydrogen. Thus, it decomposes water only slowly at 25°C whereas sodium does so vigorously, potassium reacts producing a flame and rubidium and cesium do so explosively.
- Lithium is the only alkali metal which reacts with nitrogen to give lithium nitride,Li3 N.
- Lithium hydride, LiH, is much more stable than any other hydride. Its heat of formation is the highest. However, lithium combines with hydrogen at 700-800°C whereas the other alkali metals do so at 350°-430°C. Thus, Lithium is not so reactive towards hydrogen as the other alkali metals although its hydride is most stable.
- Lithium reacts with bromine very slowly. Other alkali metals react violently.
- When burnt in air or oxygen, lithium gives only the monoxide Li2O which does not react further to give higher oxides. However, the rest of the metals give the peroxides, M2O2.
- Potassium, rubidium and cesium also give the superoxides, MO2
- Lithium hydroxide decomposes at red heat forming Li2O. The other alkali metal hydroxides do not decompose even at red heat. Also, lithium hydroxide has the lowest solubility among the hydroxides of the alkali metals.
- The carbonate of lithium is thermally less stable and decomposes into oxide on moderate heating. Li2O +CO2
- Its monoxide, Li2O, is much less basic than the oxides of other alkali metals. Also, it dissolves in water much less readily than sodium or potassium monoxide.
- Lithium hydroxide is a much weaker base than Sodium hydroxide or potassium hydroxide. Its solubility is comparable with that of calcium hydroxide.
- Lithium fluoride, phosphate, oxalate and carbonate are sparingly soluble in water like the corresponding salts of magnesium. The corresponding salts of sodium and potassium are freely soluble in water.
- Lithium chloride and lithium nitrate are soluble in alcohol while the corresponding salts of other alkali metals are insoluble in alcohol.
- Bromide and iodide of lithium are soluble in organic solvents. The corresponding salts of sodium and potassium are not soluble.
- Lithium chloride separates out from aqueous solution as hydrated crystals, LiCl.2H2O. Sodium and other alkali metal chlorides do not form hydrates at ordinary temperatures. Lithium chloride is deliquescent.
- Lithium chloride undergoes hydrolysis in hot water though to a small extent but sodium and potassium chlorides do not hydrolysis.
- Lithium nitrate evolves nitrogen dioxide and oxygen on leaving behind lithium oxide.
- Lithium sulphate, Li2SO4, unlike sulphates of other alkali metals, does not form alums.
- Lithium ion has a high polarizing power. The Li ion polarizes the electron charge cloud of water molecules more effectively than is done by other alkali metal ions. The Li ion is, therefore, most extensively hydrated. The degree of hydration decreases with increase in the ionic size as we move from Li to Cs. For the same reason, several lithium salts are hydrated
Diagonal Relationship of Lithium with
Magnesium:
- Lithium differs from the rest of its family members in many respects. However, it shows resemblance with magnesium, the second element of Group II. This is a case of diagonal relationship in which the first element of a group shows similarities with the second element in the next higher group in the next period, as indicated below.
Lithium resembles magnesium in several
respects as illustrated below.
- Atomic radius of lithium is 1.34 A while that of magnesium, being 1.364 A, is not very much different.
- The radii of Li+ ion (0.60 A) and Mg2+ ion (0.65 A) are not much different from each other.
- Polarising powers of Li+ ion and Mg2+ ion are about the same.
- Electronegativities of Li and Mg, being 1.0 and 1.2, respectively, are not much different from each other.
- Like magnesium, lithium decomposes water only slowly liberating hydrogen.
- Like magnesium, lithium hardly reacts with liquid bromine.
- Lithium reacts with nitrogen to give lithium nitride, Li3N. Magnesium also reacts with nitrogen to give magnesium nitride, Mg3N2
- Lithium hydroxide, like magnesium hydroxide, is very slightly soluble in water.
- Lithium hydroxide, like magnesium hydroxide, is a weak base.
- Lithium fluoride, phosphate, oxalate and carbonate, like the corresponding salts of magnesium, are sparingly soluble in water.
- Lithium chloride, like magnesium chloride, separates out from aqueous solutions as hydrated crystals, LiCl.2H2O.
- Lithium chloride, like magnesium chloride, is deliquescent.
- Lithium chloride, like magnesium chloride, undergoes hydrolysis in hot water though to a smaller extent than magnesium chloride.
- Lithium, nitrate, like magesium nitrate, evolves nitrogen dioxide and oxygen on heating, leaving behind the oxide.
4LINO3 → 2Li2O + 4NO2
+ O2
2Mg(NO3)2 → 2MgO + 4NO2
+ O2
- Lithium forms only the monoxide, Li2O. Magnesium also prefers to form only the monoxide, MgO.
