Reactivity

Although increasing reactivity predicts increasingly vigorous reactions down the group, the difference may be less obvious in demonstrations with oxygen or chlorine than it is with water.

To deduce relative reactivity, you use observations to decide which of two metals is more reactive, then combine those comparisons into an order. The comparison must be fair: a large piece of metal may appear to react faster than a small piece simply because more surface is exposed.

Reaction behaviour is similar within a group, but reactivity can change down the group. Down Group 1, the outer electron is farther from the nucleus and is easier to lose, so reactivity increases. Down Group 7, an incoming electron is attracted less strongly as the outer shell becomes farther from the nucleus, so reactivity decreases.

Finally, apply the direction of the group’s reactivity trend.