Periodic trends

Atomic radius

The distance from the atom's nucleus to the outer edge of the electron cloud.

Trend of atomic radius across a period

Decreases as effective nuclear charge increases.

Trend of atomic radius down a group

Increases due to the increase in the number of energy levels.

Effective nuclear charge

The net positive charge experienced by an electron in a multi-electron atom.

Cation

A positively charged ion that has lost one or more valence electrons, resulting in a smaller radius than its neutral atom.

Anion

A negatively charged ion that has gained one or more valence electrons, resulting in a larger radius than its neutral atom.

Ionic radius

The distance from the nucleus to the outer edge of the electron cloud of an ion.

Trend of ionization energy across a period

Increases due to increasing effective nuclear charge.

Trend of ionization energy down a group

Decreases due to increased distance between the nucleus and highest-energy electron.

Ionization energy (IE)

The energy required to remove the highest-energy electron from a neutral atom.

Electronegativity

The measure of the ability of an atom in a bond to attract electrons to itself.

Trend of electronegativity across a period

Increases as atoms tend to gain electrons.

Trend of electronegativity down a group

Decreases due to increased distance and shielding.

Most electronegative element

Fluorine.

Least electronegative element

Francium.