Down the group · Year 9 Science

Down the groupPick a group · step down it one element at a time

Lithium (2 shells), sodium (3), potassium (4): the outer electron is further out each time, so it is held less tightly and lost more easily. Reactivity increases down Group 1.
Fluorine (2 shells), chlorine (3), bromine (4), iodine (5): an incoming electron would sit further out each time, where the pull is weaker, so it is gained less easily. Reactivity decreases down Group 17.

Choose a group: