Why does the reactivity of the Group 1 elements increase as you go down the group?

As you descend group 1, there is an increasing number of electron shells, therefore increasing the distance between the positive nucleus and the negative outer electron which decreases the attraction between the two. Due to the group 1 elements forming ionic compounds, they lose their outer electron when they react and so the weaker attraction between the nucleus and the outer electron means they are able to lose that electron more easily and therefore are more reactive.