Periodic properties are properties of elements that show a regular pattern (trend) across periods and down groups in the periodic table.

Examples:

• Atomic radius: decreases across a period, increases down a group.
• Ionization enthalpy: increases across a period, decreases down a group.
• Electron gain enthalpy: becomes more negative across a period (till group 17).
• Electronegativity: increases across a period, decreases down a group.
• Valency: shows a definite trend based on group number.