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

Outer electrons of Group 1

The electronic configuration will show the outer electrons.

Li 2.1
Na 2.8.1
K 2.8.8.1

The outer shell has only one electron in (as these elements are in group 1).
When these elements react they lose their outer electron. In order to lose an electron, the atom requires energy to overcome the electrostatic forces of attraction between the negatively charged electron and the positively charged nucleus.

K is the most reactive element of these 3 metals because less energy is required to remove the outer electron from its atom, that is required for sodium and lithium.