Periods and Groups Definition, Types, Examples & Uses

Periods and Groups

Subject: Chemistry

Book: General Chemistry

The periodic table is structured in periods (horizontal rows) and groups (vertical columns). Periods indicate the principal energy level for the element’s valence electrons. Groups, often labeled 1–18 or by names (e.g., Group 1: Alkali Metals), contain elements with similar valence electron configurations and thus similar chemical properties. For example, Group 17 (the halogens) are highly reactive nonmetals. Understanding periods and groups is vital for predicting reactivity, trends in atomic size, and more.