Periods are the columns of the periodic table that go vertically. Families are the rows that go across.
Work Step by Step
By looking at the Periodic Table of Elements, an example of a period would be the row starting with Potassium and ending in Krypton. You can remember periods go across horizontally because a sentence goes across the page horizontally and you end sentences with a period. Family Trees go down vertically so Families go vertically on the periodic table.