Trends

Electron Affinity

• Definition:
  The energy change that occurs when an atom gains an electron to form a negative ion.

• Across a Row (→):
  Increases (becomes more negative)
  → Atoms more strongly attract extra electrons as nuclear charge increases.

• Down a Column (↓):
  Decreases
  → Added electrons enter higher energy levels farther from the nucleus, so the attraction is weaker.

Ionization Energy

• Definition:
  The energy required to remove one electron from a neutral atom in the gaseous state.

• Across a Row (→):
  Increases
  → Atoms hold electrons more tightly due to stronger nuclear charge.

• Down a Column (↓):
  Decreases
  → Electrons are farther from the nucleus and easier to remove.

Ionic Radius

• Definition:
  The size of an ion (positive or negative).

• Across a Row (→):

  • For cations (+): Radius decreases due to loss of electrons and stronger pull on remaining electrons.

  • For anions (−): Radius decreases across because of increasing nuclear charge pulling electrons in tighter.

• Down a Column (↓):
  Increases
  → More energy levels are added, making the ions larger.

Atomic Radius

• Definition:
  The distance from the nucleus to the outermost electron orbital of an atom.

• Across a Row (→):
  Decreases
  → Electrons are added to the same shell, but nuclear charge increases, pulling electrons closer.

• Down a Column (↓):
  Increases
  → More electron shells are added, increasing the size.