Trends in Electronegativity (CIE AS Chemistry)

• Electronegativity varies across Periods and down the Groups of the Periodic Table

Down a group

• There is a decrease in electronegativity going down the Group
• The nuclear charge increases as more protons are being added to the nucleus
• However, each element has an extra filled electron shell, which increases the shielding
• The addition of the extra shells increases the distance between the nucleus and the outer electrons resulting in larger atomic radii
• Overall, there is a decrease in attraction between the nucleus and outer bonding electrons

Why electronegativity decreases down a group

Electronegativity decreases going down the groups of the periodic table

Across a period

• Electronegativity increases across a Period
• The nuclear charge increases with the addition of protons to the nucleus
• Shielding remains reasonably the same across the Period as no new shells are being added to the atoms
• The nucleus has an increasingly strong attraction for the bonding pair of electrons of atoms across the Period of the Periodic Table
• This results in smaller atomic radii

Why electronegativity increases across a period

Electronegativity increases going across the periods of the Periodic Table

Trends down a group & across a periodic table

	Down a group	Across a period
Nuclear charge	Increases	Increases
Shielding	Increases	Reasonably constant
Atomic radius	Increases	Decreases
Electronegativity	Decreases	Increases