Question

The increasing order of reactivity among group 1 element is $Li<Na<Rb<Cs$, whereas that among group 17 element is $F>CI>Br>I$. Explain?

Answer 1

Group 1 elements contain one electron in the valence shell. They have strong tendency to lose valence electron. The tendency to loose valence electron depends upon the ionization enthalpy. On moving down the group, the ionization enthalpy decreases. Due to this, the reactivity of the group increases in the same order $Li<Na<K<Rb<Cs$.

In the valence shell of group 17 elements, 7 electrons are present. They have strong tendency to accept on more electron. This tendency depends upon the electrode potentials of group 17 elements which decreases from F to I. Their reactivities also decreases in the same order $F>Cl>Br>I$.