Why is water and sodium so reactive?

Sodium (Na; Atomic number: 11) is a higly reactive element belonging to the alkali group. Since sodium has valency 1 ie it has one lone electron in its outermost orbital, it is highly reactive in nature. When sodium is added to water, the lone electron of sodium reacts with the hydroxyl group of water and displaces H+ ion, thus forming NaOH (sodium hydroxide). Since this is a highly exothermic reaction, the sudden release of energy during bond reformation results in explosion.