Periodic Table Trends

Atomic Radius

The distance from the nucleus to the outermost shell of an electron.

Trend Across a Period for Atomic Radius

Decreases because increasing nuclear charge pulls electrons closer.

Trend Down a Group for Atomic Radius

Increases due to the addition of electron shells.

Ionization Energy (IE)

The energy required to remove an electron from an atom.

Trend Across a Period for Ionization Energy

Increases due to stronger nuclear attraction.

Trend Down a Group for Ionization Energy

Decreases because outer electrons are farther from the nucleus.

Electronegativity

Ability of an atom to attract electrons in a bond.

Trend Across a Period for Electronegativity

Increases (except noble gases) as atoms want to gain electrons.

Trend Down a Group for Electronegativity

Decreases because larger atoms have a weaker pull on bonding electrons.

Most Electronegative Element

Fluorine (F).

Electron Affinity

The energy change when an atom gains an electron.

Trend Across a Period for Electron Affinity

Generally increases (becomes more negative) because of octet completion.

Trend Down a Group for Electron Affinity

Decreases because larger atoms have a weaker attraction for additional electrons.

Metallic Character

How easily an element loses electrons.

Trend Across a Period for Metallic Character

Decreases as elements become more nonmetallic.

Trend Down a Group for Metallic Character

Increases because atoms lose electrons more easily.

Reactivity of Metals

Increases down a group and decreases across a period.

Reactivity of Nonmetals

Decreases down a group and increases across a period (except noble gases).

Shielding Effect

Core electrons block valence electrons from the nuclear pull.

Trend Across a Period for Shielding Effect

Stays relatively constant.

Trend Down a Group for Shielding Effect

Increases due to more electron shells.

Effective Nuclear Charge (Z_eff)

Net positive charge experienced by valence electrons.

Trend Across a Period for Z_eff

Increases as protons increase.

Trend Down a Group for Z_eff

Decreases due to more shielding.

Mnemonics for Atomic Radius

“Bigger as you go down, smaller as you go across.”

Mnemonics for Electronegativity

“E.N. is FON (Fluorine, Oxygen, Nitrogen).”

Mnemonics for Ionization Energy

“IE follows E.N.” (Higher electronegativity = higher ionization energy).