Why does lithium differ from other alkali metals?

(N/A) $(i)$ Lithium is much harder. Its melting point $(m.p.)$ and boiling point $(b.p.)$ are higher than the other alkali metals.
$(ii)$ Lithium is the least reactive but the strongest reducing agent among all the alkali metals. On combustion in air,it forms mainly monoxide,$Li_{2}O$,and the nitride,$Li_{3}N$,unlike other alkali metals.
$(iii)$ $LiCl$ is deliquescent and crystallises as a hydrate,$(LiCl \cdot 2H_{2}O)$,whereas other alkali metal chlorides do not form hydrates.
$(iv)$ Lithium hydrogen carbonate is not obtained in the solid form,while all other elements form solid hydrogen carbonates.
$(v)$ Lithium,unlike other alkali metals,forms no ethynide on reaction with ethyne.
$(vi)$ Lithium nitrate when heated gives lithium oxide $(Li_{2}O)$,whereas other alkali metal nitrates decompose to give the corresponding nitrite.
$4LiNO_{3} \rightarrow 2Li_{2}O + 4NO_{2} + O_{2}$
$2NaNO_{3} \rightarrow 2NaNO_{2} + O_{2}$
$(vii)$ $LiF$ and $Li_{2}O$ are comparatively much less soluble in water than the corresponding compounds of other alkali metals.