Trends in Electronegativity (Cambridge International A-Level Chemistry)

Spec point — 3.1.3

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

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 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

Exam Hint

• Remember the general trend is an increase in electronegativity towards the top right of the Periodic Table.
• Fluorine is the most electronegative element in the Periodic Table.