In the periodic table, the maximum chemical reactivity is at the extreme left (alkali metals) and extreme right (halogens). Which properties of these two groups are responsible for this?

High chemical reactivity of alkali metals is due to low ionisation energies. Alkali metals readily lose an electron and form cation with stable noble gas electronic configuration. High chemical reactivity of halogens is due to high negative electron gain enthalpies. Halogens readily accept an electron and form anion with stable noble gas electronic configuration.