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

Group 1 elements contain one electron in the valence shell. They have a strong tendency to lose valence electrons. The tendency to lose valence electrons 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 a strong tendency to accept one more electron. This tendency depends upon the electrode potentials of group 17 elements which decreases from F to I. Their reactivities also decrease in the same order F>Cl>Br>I.