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ChemistryA Level & IB

What is electronegativity?

Electronegativity is the ability of an atom to attract the shared pair of electrons in a covalent bond towards itself.

Electronegativity explained

It increases across a period as nuclear charge rises, and decreases down a group as the bonding electrons sit further from the nucleus and are shielded.
A difference in electronegativity produces a polar bond, and if the molecular shape does not cancel those dipoles the whole molecule is polar.

Key formula

Δχ\Delta\chi large ⇒\Rightarrow ionic; small ⇒\Rightarrow polar covalent

Worked example

In H–Cl the chlorine is more electronegative, so the bond is polar with δ+ on hydrogen and δ− on chlorine.

Examiner tip

A molecule with polar bonds can still be non-polar overall — CO₂ is the standard example because its dipoles cancel by symmetry.

Electronegativity: common questions

Which element is the most electronegative?
Fluorine, followed by oxygen, nitrogen and chlorine.
How does electronegativity affect hydrogen bonding?
Hydrogen bonded to N, O or F becomes strongly δ+, allowing an attraction to a lone pair on a neighbouring molecule.

Related terms

Covalent bond

A covalent bond is a shared pair of electrons between two non-metal atoms, held together by attraction to both nuclei.

Ionic bond

An ionic bond is the strong electrostatic attraction between oppositely charged ions formed when electrons transfer from a metal to a non-metal.

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