Anomalous behaviour of Lithium is due to
1) very small size of lithium atom and its ions.
2) higher polarising power of Li+ resulting in increased covalent character of its compounds which is responsible for their solubility in organic solvents.
3) comparatively high ionization enthalpy and low electropositive character of lithium as compared to other alkali metals.
4) non availability of d orbitals in its valence shell
5) strong inter metallic bonding
Properties in which Lithium differ from the other member of its groups are
1) Lithium is harder while all other alkali metals are soft.
2)The melting and boiling point of lithium are comparatively high.
3) Lithium forms monoxides with oxygen while other alkali metals from peroxides as well as superoxide.
4) When burnt in air or nitrogen, lithium forms Lithium nitride due to its high lattice energy. The Other alkali metals do not form their corresponding nitrides because their lattice energies decreases as their size increases from Na to Cs.
6 Li + N2 —–> 2 Li3N
5) LiOH is a weak base while the hydroxides of other alkali metal are strong bases.
6) The hydrides of Lithium is more stable than hydrides of other alkali metals.
7) Lithium hydroxide on heating decompose to form lithium oxide while other alkali metal hydroxides do not
2 LiOH ——> Li2O + H2O
8) lithium carbonate on heating decomposes to CO2 while other alkali metal carbonates do not
Li2CO3 ——> Li2O + CO2
9) Lithium bicarbonate does not form a solid though it exists in solution while all other alkali metal from solid bicarbonates.
10) Lithium does not react with ethyne to form lithium ethynide while all the other alkali metals react to form the corresponding alkynides.
2 Na + HC≡CH ———> Na+ C≡C Na+ + H2
When Lithium is heated with carbon, its forms dilithium acetylide while other alkali metals do not react with carbon directly.
2 Li+ 2 C ——–> Li+ C≡C Li+
11) Lithium nitrate on heating decomposes to give Li2O , NO2 and O2 while other alkali metal nitrates decompose to give the corresponding nitrite and oxygen.
4 LiNO3 ——-> 2 Li2O + 4 NO2 + O2
2 NaNO3 ——-> 2 NaNO2 + O2
12) The oxides, hydroxides, carbonates, phosphate ,oxalate and fluoride of lithium are sparingly soluble in water whereas the corresponding salts of other alkali metals are soluble in water.
13) Because of the covalent character, halides of lithium are soluble in organic solvents such as alcohol, acetone ,pyridine while those of other alkali metals are insoluble.
14) LiCL is deliquescent and crystallizes as a hydrate, LiCl·2H2O , whereas other alkali metal chlorides do not form hydrates.
15) Lithium ion ,being very small in size is very strongly hydrated in aqueous solution as compared to other alkali metal ions that is why effective size of ion in aqueous solution is the largest and hence its mobility is the lowest.
16) Li2SO4 is the only alkali metal sulphate which does not form an alum.
17) Lithium when heated with NH3 forms Lithium imide, Li2NH while all of the alkali metals form amides, MNH2.