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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Electronegativity difference (ΔEN)

The absolute difference between the electronegativities of two bonded atoms, ΔEN=∣ENA−ENB∣\Delta\text{EN} = \left|\text{EN}_A - \text{EN}_B\right|. It classifies the bond: below 0.4 nonpolar covalent, 0.4 to below 1.8 polar covalent, 1.8 or more ionic (this course's cut-offs).

From nonpolar covalent to ionicBond type depends on the electronegativity difference ΔEN. Cl–Cl (ΔEN 0) shares electrons equally: nonpolar covalent. H–Cl (ΔEN ≈ 1.0) shares unequally: polar covalent. Na⁺Cl⁻ (ΔEN ≈ 2.1) transfers an electron: ionic. Course cut-offs: below 0.4 nonpolar, 1.8 and above ionic.ClClshared equallyHClδ+δ−shared unequallyNa⁺Cl⁻e⁻ transferred00.41.83nonpolarpolar covalentionicΔEN (electronegativity difference)

Bond character changes gradually as ΔEN\Delta\text{EN} grows.

Example

Mg–O: 3.44−1.31=2.133.44 - 1.31 = 2.13, ionic. S–O: 3.44−2.58=0.863.44 - 2.58 = 0.86, polar covalent.

See alsoElectronegativityIonic bondPolar covalent bondNonpolar covalent bond