Find the element’s group number on the periodic table
For main-group elements, the group number shows the number of valence electrons
Group 1 elements have 1 valence electron
Group 2 elements have 2 valence electrons
Groups 13 through 18 have 3 through 8 valence electrons
Subtract 10 from the group number for groups 13 through 18
Helium has 2 valence electrons
Transition metals do not follow a simple group-number rule for valence electrons