chemistry questions!

(a)
Among the metal ions of the Group I elements, Li+ has the smallest size, and thus the greatest charge density (charge-to-volume ratio). The cation with a higher charge density can polarize the anion to a greater extent. In an ionic compound, the more the anion is polarized, the higher is the extent that the electron cloud is withdrawn from the anion and to the cation, and thus the higher is the covalent character.

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(b)
In group I, all the elements have giant metallic structure in which the atoms are held together by metallic bonds. In each Group I metal, the metal bonds contain 1 delocalized electron per metal ion. Down the group, the atomic size is increasing due to the increase in number of filled electron shells. This will lead to the decreasing in melting point down the group, because of the decreasing in the strength of attractions between the atomic nuclei and the delocalized electrons, as their average distance is increasing.

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(c)
(i) 2Na(s) + 2H2O(l) → 2Na+(aq) + 2OH-(aq) + H2(g)

(ii) 2Li(s) + 2H2O(l) → 2Li+(aq) + 2OH-(aq) + H2(g)

(iii) 2Rb(s) + I2(s/g) → 2RbI(s)
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