Periodic Trends New

What is atomic radius?

Distance from the nucleus to the outermost electron.

What is the trend for atomic radius across a period and down a group?

Decreases across, increases down. (DA, ID)

Why does atomic radius decrease across a period?

Z_eff increases, pulling electrons in tighter. More shells are added down a group.

What is ionization energy?

Energy required to remove an electron from a gaseous atom.

What is the trend for ionization energy across a period and down a group?

Increases across, decreases down. (IA, DD)

Why does ionization energy increase across a period?

Z_eff increases, so electrons are held more tightly. Electrons are farther from the nucleus down a group, so easier to remove.

What is electron affinity?

Energy change when an atom gains an electron.

What is the trend for electron affinity across a period and down a group?

More negative across, no strong trend down. (IA, NT)

Why does electron affinity become more negative across a period?

Atoms have higher Z_eff and want to fill their valence shells.

What is ionic radius?

Size of an ion compared to its neutral atom.

What is the trend for ionic radius across a period and down a group?

Decreases across a period (for same charge), increases down. (DA, ID)

Why are cations smaller and anions larger than their neutral atoms?

Cations lose electrons → less repulsion; anions gain electrons → more repulsion.

What is effective nuclear charge (Z_eff)?

The net pull on valence electrons from the nucleus. (Z_eff = Z - S)

What is the trend for Z_eff across a period and down a group?

Increases across, slightly decreases down. (IA, DD)

Why does Z_eff increase across a period?

More protons, but same shielding → stronger nuclear pull.

What is electronegativity?

An atom’s ability to attract electrons in a bond.

What is the trend for electronegativity across a period and down a group?

Increases across, decreases down. (IA, DD)

Why does electronegativity increase across a period?

Z_eff increases → stronger attraction for bonding electrons.

What is metallic character?

Tendency of an atom to lose electrons and behave like a metal.

What is the trend for metallic character across a period and down a group?

Decreases across, increases down. (DD, ID)

Why does metallic character increase down a group?

Electrons are farther from the nucleus → easier to lose.

What is the shielding effect?

When inner/core electrons block the attraction between the nucleus and valence electrons.

What is the trend for shielding across a period and down a group?

Constant across a period, increases down a group. (C, ID)

Why does shielding increase down a group?

More inner shells are added, blocking nuclear pull on outer electrons.