(i) Name the groups which constitute s-block elements.
(ii) Why cannot sodium and potassium be prepared by the electrolysis of their aqueous solutions?
(iii) Why is the density of potassium less than sodium?
(iV) Why are alkali metals soft and have low melting points?
(v) What happens when K burns in air? Give chemical equation.
(i) r-block contains only two groups; group 1 (alkali metals) and group 2 (alkaline earth metals).
(ii) The electrode potential, i.e., reduction potential of Na (— 2.71 V) or K (— 2.92) is much lower than that of $H { 2 }O$(—0.83V), therefore, upon electrolysis, water gets reduced in preference to ${{Na}^{+}}$ or ${{K}^{+}}$ ions.
In other words, sodium and potassium cannot be obtained by electrolytic reduction of Na+ and K+ ions in aqueous solution.
(iii) This is due to abnormal increase in the atomic size of potassium.
(iv) Alkali metals have only one valence electron per metal atom. As a result, the binding energy of alkali metal ions in the close-packed metal lattices are weak. Therefore these are soft and have low melting points.
(v) K +${{O}{2}}$ —»
K ${{O}_{2}}$, potassium superoxide will be formed.