In what ways lithium shows similarities to magnesium in its chemical behaviour?

Solution:

Similarities between lithium and magnesium are as follows.

(i) Both Li and Mg react slowly with cold water.

(ii) The oxides of both Li and Mg are much less soluble in water and their hydroxides decompose at high temperature.

$2 \mathrm{LiOH} \stackrel{\text { heat }}{\longrightarrow} \mathrm{Li}_{2} \mathrm{O}+\mathrm{H}_{2} \mathrm{O}$

$\mathrm{Mg}(\mathrm{OH})_{2} \stackrel{\text { heat }}{\longrightarrow} \mathrm{MgO}+\mathrm{H}_{2} \mathrm{O}$

(iii) Both Li and Mg react with N2 to form nitrides.

$6 \mathrm{Li}+\mathrm{N}_{2} \stackrel{\text { heat }}{\longrightarrow} 2 \mathrm{Li}_{3} \mathrm{~N}$

$3 \mathrm{Mg}+\mathrm{N}_{2} \stackrel{\text { heat }}{\longrightarrow} \mathrm{Mg}_{3} \mathrm{~N}_{2}$

(iv) Neither Li nor Mg form peroxides or superoxides.

(v) The carbonates of both are covalent in nature. Also, these decompose on heating.

$\mathrm{Li}_{2} \mathrm{CO}_{3} \stackrel{\text { heat }}{\longrightarrow} \mathrm{Li}_{2} \mathrm{O}+\mathrm{CO}_{2}$

$\mathrm{MgCO}_{3} \stackrel{\text { heat }}{\longrightarrow} \mathrm{MgO}+\mathrm{CO}_{2}$

(vi) Li and Mg do not form solid bicarbonates.

(vii) Both $\mathrm{LiCl}$ and $\mathrm{MgCl}_{2}$ are soluble in ethanol owing to their covalent nature.

(viii) Both $\mathrm{LiCl}$ and $\mathrm{MgCl}_{2}$ are deliquescent in nature. They crystallize from aqueous solutions as hydrates, for example, $\mathrm{LiCl} \cdot 2 \mathrm{H}_{2} \mathrm{O}$ and $\mathrm{MgCl}_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}$.