2.8 Explain the relative reactivities of the elements in Group 1 in terms of distance between the outer electrons and the nucleus.

Group 1 elements only have 1 electron in their outer shell. Electrons are held to the atom by the forces of attraction between the nucleus (which has protons, so a positive charge) and the electrons themselves (which have a negative charge). If there are more shells, the last electron (which will be lost if the metal reacts with anything)  is further away from the nucleus, so the forces of attraction between the nucleus and the electron are weaker. The more shells, the further away, and it's more reactive.

As you go down the group, they become more reactive because there is an increase in the number of shells :)

(Does this make sense or am I talking gibberish?)