Periodic Trends

Atomic Radius - Definition

Distance from nucleus to outermost electron.

Atomic Radius - Trend

DA, ID

Atomic Radius - Why

Zₑff increases across, pulling electrons closer. More shells added down.

Ionization Energy - Definition

Energy to remove an electron from a gaseous atom.

Ionization Energy - Trend

IA, DD

Ionization Energy - Why

Zₑff increases across → harder to remove e⁻. Electrons are farther down = easier to remove.

Electron Affinity - Definition

Energy change when an atom gains an electron.

Electron Affinity - Trend

IA, NT

Electron Affinity - Why

Atoms want to fill valence shells more across. No consistent trend down.

Ionic Radius - Definition

Size of an ion vs. its atom.

Ionic Radius - Trend

DA (within a charge group), ID

Ionic Radius - Why

More protons = tighter pull. More shells = larger ions down group.

Effective Nuclear Charge - Definition

Net nuclear pull on valence electrons. (Z_eff = Z - S)

Effective Nuclear Charge - Trend

IA, DD (slight)

Effective Nuclear Charge - Why

More protons across, shielding stays same. Slightly more shielding down.

Electronegativity - Definition

Atom’s ability to attract electrons in a bond.

Electronegativity - Trend

IA, DD

Electronegativity - Why

Zₑff increases → stronger attraction. Bigger atoms down → weaker pull.

Metallic Character - Definition

Tendency to lose electrons (metal behavior).

Metallic Character - Trend

DD, ID

Metallic Character - Why

Electrons are easier to remove down, harder across.

Shielding Effect - Definition

Core electrons block nuclear pull on valence electrons.

Shielding Effect - Trend

C, ID

Shielding Effect - Why

Across = same # of inner e⁻. Down = more shells added.