Explain the following:
a. Despite the fact that `Li^(o+)` has the smallest size among alkali metals, it moves through a solution less rapidly than the others.
b. LiF has the lowest solubility among group 1 metal haldes.
c. The softness of alkali metals increases with the increases in atomic number.

Explanation

a. `Li^(o+)` ion has the highest charge density (charge/radius ration) and hence it has maximum degree of hydration. As a result, the size of hydrated `Li^(o+)` ion is the largest and it moves less rapidly than the other smaller hydrated alkali metal ions through aqueous solution.
b. LiF has very high lattice because of the small size of both `Li^(o+)` and `F^(Θ)` ions. This high lattice energy is not compensated by hydration energy of LiF and hence LiF has the lowest solubility of group 1 metal halides.
c. Alkali metals have only one electron per larger-sized metal atom and hence the strenght of metallic bond is low. Thus, alkali metals are soft in nature. Down the group `(darr)` as the atomic number increases, the atomic size also increases. This leads to weakening of the strength of metalic bond and hence softness increases.