What do the elements in each column of the periodic table have in common?

Valency - Number of outermost electrons

Explanation:

Periodic table are generally divided into rows and columns.

Each columns in the periodic table is referred to as groups. Each groups represent the valency of the element. That is, the total number of outermost electrons. Due to the same number of valency, elements in the same group show similar chemical properties.

This means that group 1 elements have a valency of 1, group 2 elements have a valency of 2.