Elements in the same group have the same number of valence electrons.
- Elements in the same group are those that are in a single vertical line from top to bottom.
- They share the same number of electrons in their valence subshells.
- Elements in the same period are those that are in a single horizontal line from left to right.
- For example, period 5 elements have their electrons filling them up to the fifth energy shell and period 6 elements have electrons that go to the sixth energy shell.
- Chlorine and Bromine are kept in the same group as they have the same number of valence electrons and exhibit similar chemical behaviour.
