# What do all the elements in a horizontal column of the periodic table have in common?

Dec 1, 2016

Columns on the Periodic Table dictate the same valence electronic shell, i.e. the same electronic shell. The number of the columns, which chemists call $\text{Groups}$ is the number of valence electrons. I am simpliflying this a bit, but this is the way the Periodic Table is constructed.