A period is horizontal; the elements gain 1 proton for each space moving left to right. A group is vertical; the elements in each group have the same number of electrons in the valence shell(outer orbital).
In the periodic table, the vertical columns are called the “groups” or sometimes referred as “families.” They are called this because they have similar chemical properties. The horizontal rows on the period table are called periods because they all have same exact number of electron shells.
