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.