As you go across the periodic table there is 1 more electron in the outer ring in each column.
Column 1, all have 1 electron in the outer ring
Column 2, all have 2 electrons in the outer ring
column 3, all have 3 electrons in the outer ring
Etc.
Each row going down has 1 more ring of electrons.
Row 1 with H and He has 1 ring
row 2 has 2 rings
row 3 has 3 rings
etc.
