Trends in Electronegativity (Cambridge (CIE) A Level Chemistry): Revision Note

Trends in Electronegativity

• 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

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

Trends down a group & across a period

• Nuclear charge

  • Increases down a group

  • Increases across a period

• Shielding

  • Increases down a group

  • Reasonably constant across a period

• Atomic radius

  • Increases down a group

  • Decreases across a period

• Electronegativity

  • Decreases down a group

  • Increases across a period