Question

The increasing order of reactivity for first group element is Li < Na < K < Rb < Cs where as for group 17 It is as F > Cl > Br > J. Explain it .

Answer 1

The reactivity in first group elements occur due to the tendency of electron releasing which is measured by ionization enthalpy. The ionization enthalpy decreases

when we move down to the group thus reactivity of metals increases.

Reactivity of metals = \(\frac{1}{\text{Ionization}\ \text{enthalpy}}\)

So order will be Li< Na < Rb < Cs.

The reactivity of halogens depends on the tendency of formation, of anions on moving down in the group as value’ of electron gain enthalpy decreases so the reactivity of halogens decreases. The reactivity of non-metals  electron gain enthalpy. So order will be F > Cl > Br > I.