Atomic Radius & Trends in the Periodic Table

Atomic Radius

• Definition: The distance from the center of the nucleus to the outermost electron in an atom.
• Units: Typically measured in picometers (pm) or angstroms (Å).

Trends in Atomic Radius

• Across a Period:
  • Decreases from left to right due to increasing nuclear charge and relatively constant shielding.
  • Electrons are pulled closer to the nucleus as the number of protons increases.
• Down a Group:
  • Increases due to the addition of energy levels and increasing shielding.
  • The outermost electrons are farther from the nucleus as the atomic number increases.

Factors Affecting Atomic Radius

• Nuclear Charge: As the number of protons increases, the nuclear charge increases, pulling electrons closer to the nucleus.
• Shielding: The ability of inner electrons to shield outer electrons from the nuclear charge, resulting in a larger atomic radius.
• Number of Electron Shells: As the number of electron shells increases, the atomic radius increases due to the additional energy levels.

Importance of Atomic Radius

• Chemical Properties: Atomic radius influences chemical properties such as reactivity, electronegativity, and ionization energy.
• Physical Properties: Atomic radius affects physical properties such as melting and boiling points, density, and atomic volume.

Atomic Radius

• Atomic radius is the distance from the center of the nucleus to the outermost electron in an atom.

Units of Atomic Radius

• Atomic radius is typically measured in picometers (pm) or angstroms (Å).

Trends in Atomic Radius

Across a Period

• Atomic radius decreases from left to right across a period due to increasing nuclear charge and relatively constant shielding.
• Electrons are pulled closer to the nucleus as the number of protons increases.

Down a Group

• Atomic radius increases down a group due to the addition of energy levels and increasing shielding.
• The outermost electrons are farther from the nucleus as the atomic number increases.

Factors Affecting Atomic Radius

• Increasing nuclear charge pulls electrons closer to the nucleus, decreasing atomic radius.
• Shielding by inner electrons reduces the nuclear charge, resulting in a larger atomic radius.
• The addition of electron shells increases atomic radius due to the additional energy levels.

Importance of Atomic Radius

• Atomic radius influences chemical properties such as reactivity, electronegativity, and ionization energy.
• Atomic radius affects physical properties such as melting and boiling points, density, and atomic volume.