Anomalous behaviour of lithium is due to extremely low size of lithium its cation. On account of small size and high nuclear charge, lithium exerts the greatest polarizing effect out of all alkali metals on negative ion. Consequently lithium ion possesses remarkable tendency towards solvation and develops covalent character in its compounds.
`Li` differs from other alkali metals in the following respects,
(i) It is comparatively harder than other alkali metals.
(ii) It can be melted in dry air without losing its brilliance.
(iii) Unlike other alkali metals, lithium is reactive among all. It can be noticed by the following properties,
(a) It is not affected by air.
(b) It decomposes water very slowly to liberate `N_2`.
(c) It hardly reacts with bromine while other alkali metals react violently.
(iv) Lithium is the only alkali metal which directly reacts with `N_2`.
(v) Lithium when heated in `NH_3` forms imide, `Li_2NH` while other metals form amides, `MNH_2`.
(vi) When burnt in air, lithium form `Li_2O`, sodium form `Na_2O` and `Na_2O_2`, other alkali metals form monoxide, peroxide and superoxide.
(vii) `Li_2O` is less basic and less soluble in water than other alkali metals.
(viii) `LiOH` is weaker base than `NaOH` or `KOH` and decomposes on heating.
`2LiOH overset(Delta)-> Li_2O + H_2O`
(ix) `LiHCO_3` is liquid while other metal bicarbonates are solid.
(x) Only `Li_2CO_3` decomposes on heating `Li_2CO_3 oversettext(heat)-> Li_2O+CO_2`. ` Na_2CO_3`, `K_2CO_3` etc. decompose on heating.
(xi) `LiNO_3` and other alkali metal nitrates give different products on heating
`4LiNO_3 = 2Li_2O + 4NO_2 + O_2 ; 2NaNO_3 = 2NaNO_2 +O_2`
(xii) `LiCl` and `LiNO_3` are soluble in alcohol and other organic solvents. These salts of other alkali metals are, however, insoluble in organic solvents.
(xiii) `LiCl` is deliquescent while `NaCl`, `KBr` etc. are not. Lithium chloride crystals contain two molecules of water of crystallisation (`LiCl*2H_2O`). Crystals of `NaCl`, `KBr`, `KI` etc do not conation water of crystallisation.
(xiv) `Li_2SO_4` does not form alums like other alkali metals.
(xv) `Li` reacts with water slowly at room temperature. `Na` reacts vigorously Reaction with `K`. `Rb` and `Cs` is violent.
(xvi) `Li` reacts with `Br_2` slowly. Reaction of other alkali metals with `Br_2` is fast.
(xvii) `Li_2 CO_3`, `Li_2C_2O_4`, `LiF`, `Li_3PO_4` are the only alkali metal salts which are insoluble or sparingly soluble in water.
Anomalous behaviour of lithium is due to extremely low size of lithium its cation. On account of small size and high nuclear charge, lithium exerts the greatest polarizing effect out of all alkali metals on negative ion. Consequently lithium ion possesses remarkable tendency towards solvation and develops covalent character in its compounds.
`Li` differs from other alkali metals in the following respects,
(i) It is comparatively harder than other alkali metals.
(ii) It can be melted in dry air without losing its brilliance.
(iii) Unlike other alkali metals, lithium is reactive among all. It can be noticed by the following properties,
(a) It is not affected by air.
(b) It decomposes water very slowly to liberate `N_2`.
(c) It hardly reacts with bromine while other alkali metals react violently.
(iv) Lithium is the only alkali metal which directly reacts with `N_2`.
(v) Lithium when heated in `NH_3` forms imide, `Li_2NH` while other metals form amides, `MNH_2`.
(vi) When burnt in air, lithium form `Li_2O`, sodium form `Na_2O` and `Na_2O_2`, other alkali metals form monoxide, peroxide and superoxide.
(vii) `Li_2O` is less basic and less soluble in water than other alkali metals.
(viii) `LiOH` is weaker base than `NaOH` or `KOH` and decomposes on heating.
`2LiOH overset(Delta)-> Li_2O + H_2O`
(ix) `LiHCO_3` is liquid while other metal bicarbonates are solid.
(x) Only `Li_2CO_3` decomposes on heating `Li_2CO_3 oversettext(heat)-> Li_2O+CO_2`. ` Na_2CO_3`, `K_2CO_3` etc. decompose on heating.
(xi) `LiNO_3` and other alkali metal nitrates give different products on heating
`4LiNO_3 = 2Li_2O + 4NO_2 + O_2 ; 2NaNO_3 = 2NaNO_2 +O_2`
(xii) `LiCl` and `LiNO_3` are soluble in alcohol and other organic solvents. These salts of other alkali metals are, however, insoluble in organic solvents.
(xiii) `LiCl` is deliquescent while `NaCl`, `KBr` etc. are not. Lithium chloride crystals contain two molecules of water of crystallisation (`LiCl*2H_2O`). Crystals of `NaCl`, `KBr`, `KI` etc do not conation water of crystallisation.
(xiv) `Li_2SO_4` does not form alums like other alkali metals.
(xv) `Li` reacts with water slowly at room temperature. `Na` reacts vigorously Reaction with `K`. `Rb` and `Cs` is violent.
(xvi) `Li` reacts with `Br_2` slowly. Reaction of other alkali metals with `Br_2` is fast.
(xvii) `Li_2 CO_3`, `Li_2C_2O_4`, `LiF`, `Li_3PO_4` are the only alkali metal salts which are insoluble or sparingly soluble in water.