Diagonal Relationship of Lithium with Magnesium
The main points of similarity :
(1) Both have almost similar electronegativities.
(2) Both Li and Mg are quite hard. They are harder and lighter than other elements in their respective groups.
(3) Both LiOH and Mg(OH)2 are weak bases.
(4) Both form ionic nitrides when heated in atmosphere of Nitrogen.
6 Li + N2 → 2 Li3N
3 Mg + N2 → 2 Mg3N2
(5) The hydroxides of both lithium and magnesium decompose upon heating.
2 LiOH → Li2O + H2O
Mg(OH)2 → MgO + H2O
(6) Both lithium and magnesium combine with oxygen to form monooxide while other members of their respective groups form peroxide and superoxide.
4 Li + O2 → 2 Li2O
2 Mg + O2 → 2 MgO
The Li2O and MgO thus formed do not combine with excess O2 to form peroxide and superoxide.
(7) The carbonates of these metals decompose on heating to the corresponding oxides with the evolution of carbon dioxide.
Li2CO3 → Li2O + CO2
MgCO3 → MgO + CO2
(8) Both Lithium and magnesium do not form solid bicarbonates.
(9) Both Lithium and magnesium nitrate decompose on heating producing nitrogen dioxide.
4 LiNO3 → 2 Li2O + 4 NO2 + O2
2 Mg(NO3)2 → MgO + 4 NO2 + O2
(10) The hydroxides, carbonate, oxalates, phosphates and fluorides of both Lithium and magnesium are sparingly soluble in water.
(11) Because of the covalent character, LiCl and MgCl2 are soluble in ethanol.
(12) Both Lithium perchlorate and magnesium perchlorate are highly soluble in ethanol.
(13) LiCl and MgCl2 are deliquescent and crystallise from aqueous solution as hydrate LiCl·2 H2O and MgCl2 ·6 H2O.