Periodic trends

Science

Definition

Periodic trends are predictable patterns in element properties across the periodic table. Atomic radius decreases across a period and increases down a group. Ionization energy and electronegativity generally increase across a period and decrease down a group. These trends result from changes in nuclear charge and electron shielding.

Examples

  • Fluorine having the highest electronegativity of all elements
  • Francium having the largest atomic radius among naturally occurring elements
  • Noble gases having the highest ionization energies in their respective periods
Key Fact

Across a period: atomic radius ↓, ionization energy ↑, electronegativity ↑. Down a group: opposite.

Related Terms

Electron configuration Electronegativity Element groups Metals nonmetals metalloids

Study This Concept

Practice periodic trends with free review games in these units:

AP Chemistry Unit 1: Atomic Structure and Properties Chemistry Unit 2: The Periodic Table