Question

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

Answer 1

$\text{Similarities between lithium and magnesium}:$

i. The atomic radius of lithium is $1.52A^{\circ }$ while that of magnesium is $1.60A^{\circ }$.

ii. The ionic radius of $L{i}^{+}$ion is $0.76A^{\circ }$, which is very close to that of $M{g}^{2+}$ ion $\left(0.72A^{\circ }\right)$.

iii. Both lithium and magnesium are harder and lighter than other elements in the respective groups.

iv. Lithium and magnesium react slowly with water. Their oxides and hydroxides are much less soluble, and their hydroxides decompose on heating.

$2LiOH\stackrel{heat}{\to }L{i}_{2}O+H_{2}O$

$Mg\left(OH{)}_2\right)\stackrel{heat}{\to }MgO+H_{2}O$

v. Both form a nitride, $L{i}_{3}N$ and $M{g}_3{N}_2$, by direct combination with nitrogen.

$6Li+N_2\stackrel{heat}{\to }2L{i}_{3}N$

$3Mg+N_2\stackrel{heat}{\to }M{g}_3{N}_2$


vi. The oxides, $L{i}_{2}O$ and $MgO$ do not combine with excess oxygen to give any superoxide.

vii. The carbonates of lithium and magnesium decompose easily on heating to form the oxides and $C{O}_2$. Solid hydrogencarbonates are not formed by lithium and magnesium.

$L{i}_{2}C{O}_3\stackrel{heat}{\to }L{i}_{2}O+C{O}_2$

$MgC{O}_3\stackrel{heat}{\to }MgO+C{O}_2$


viii. Both $LiCl$ and $MgC{l}_2$ are soluble in ethanol.

ix. Both $LiCl$ and $MgC{l}_2$ are deliquescent and crystallize from aqueous solution as hydrates, $LiCl\cdot 2H_{2}O$ and $MgC{l}_2\cdot 8H_{2}O$