Question

how the the reactivity of;

1. alkali metals vary

2. halogens vary.

Answer 1

Reactivity of the alkali metals depends upon the ionization enthalpy of the metals. Since the ionization enthalpy of the alkali metals decreases with the increase in the size of the metal down the group. Therefore, the reactivity of the alkali metals increases down the group.

Reactivity of the halogens depends upon the electron affinity of the halogens. Since the electron affinity of the halogens decreases down the group due to increase in the size of the halogen atoms. Therefore, the reactivity of the halogens decreases down the group.