Ionization Energy (IE)

Definition: Energy required to remove an electron from a gaseous atom.
Across a period (L→R): IE generally increases (higher nuclear charge).
Down a group: IE generally decreases (electron farther from nucleus).

Electronegativity (EN)

Definition: Ability of an atom to attract shared electrons in a bond.
Across a period (L→R): EN generally increases.
Down a group: EN generally decreases.
Fluorine has the highest EN (3.98). Noble gases are typically excluded.

Electron Affinity (EA)

Definition: Energy change when an electron is added to a gaseous atom.
More negative EA = more energy released = greater tendency to gain an electron.
Across a period (L→R): EA generally becomes more negative (halogens most negative).
Down a group: EA generally becomes less negative.

Periodic Trends

Compare elements by ionization energy, electronegativity, or electron affinity. Pick which is higher or rank them.

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