discuss the diagonal relationship between lithium and magnesium
Answers
Similar ionisation enthalpy and electronegativity .
High polarising power
(1) Both Li and Mg are harder and higher m.pt than the other metals of their groups.
(2) Due to covalent nature, chlorides of both Li and Mg are deliquescent and soluble in alcohol and pyridine while chlorides of other alkali metals are not so.
(3) Fluorides, phosphates of Li and Mg are sparingly soluble in water whereas those of other alkali metals are soluble in water.
(4) Carbonates of Li and Mg decompose on heating and liberate CO2 Carbonates of other alkali metals are stable towards heat and decomposed only on fusion.
Li2CO3 → Li2O + CO2 ; Mg CO3 → MgO + CO2
(5) Hydroxides and nitrates of both Li and Mg decompose on heating to give oxide. Hydroxides of both Li and Mg are weak alkali.
4 LiNO3 → 2Li2O + 4NO2 + O2
2Mg(NO3)2 → 2MgO + 4NO2 + O2
2LiOH → Li2O + H2O ; Mg(OH)2 → MgO + H2O
Hydroxides of other alkali metals are stable towards heat while their nitrates give O2 and nitrite.
2KNO3 → 2KNO2 + O2
(6) Both Li and Mg combine directly with N2 to give nitrides Li3N and Mg3N2. Other alkali metals combine at high temperature, 6Li + N2 → 2Li3N; 3Mg + N2 → Mg3N2. Both the nitrides are decomposed by water to give NH3
Li3N + 3H2O → 3LiOH + NH3;
Mg3N2 + 6H2O → 3Mg(OH)2+ 2NH3