There are two different numbering systems that are commonly used to designate groups, and you should be familiar with both. These two rows are pulled out in order to make the table itself fit more easily onto a single page.Ī group is a vertical column of the periodic table, based on the organization of the outer shell electrons.

Periods 6 and 7 have 32 elements, because the two bottom rows that are separate from the rest of the table belong to those periods. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements. A new period begins when a new principal energy level begins filling with electrons.

There are seven periods in the periodic table, with each one beginning at the far left. \) (Credit: User:Cepheus/Wikimedia Commons Source: (opens in new window) License: Public Domain)Ī period is a horizontal row of the periodic table.