Question

What does each column (down) have in common?

Answer 1

The columns or groups have in common is the valence electron count. The valence electron count is the same in each row except for the transition metals.

Answer 2

Answer:

elements in each group have the same number of electrons in the outer orbital. Those outer electrons are also called valence electrons.

Every element in the second column (group two) has two electrons in the outer shell.