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Bond Polarity and Electronegativity

Sep 25, 2025

Overview

This lecture explains how to compare the polarity of covalent bonds using electronegativity differences, provides examples with common elements, and demonstrates how to rank bonds from least to most polar.

Electronegativity and Bond Polarity

  • Electronegativity (EN) measures an atom's tendency to attract bonding electrons.
  • The greater the EN difference between two bonded atoms, the more polar the bond.
  • Nonpolar covalent bonds have an EN difference less than 0.5.
  • Polar covalent bonds have an EN difference between 0.5 and 2.0.

Comparing Common Bonds

  • Carbon (EN 2.5) and hydrogen (EN 2.1) have an EN difference of 0.4, so C–H is nonpolar covalent.
  • Carbon and oxygen (EN 3.5) have an EN difference of 1.0, so C–O is polar covalent and more polar than C–H.
  • Hydrogen and oxygen (EN 3.5) have an EN difference of 1.4.
  • Hydrogen and fluorine (EN 4.0) have an EN difference of 1.9; H–F is more polar than O–H.
  • To show bond polarity, draw the dipole arrow toward the more electronegative atom, which receives a partial negative charge (δ–).

Using the Periodic Table to Estimate Polarity

  • Electronegativity increases across a period (left to right) and up a group.
  • For atoms in the same row, greater distance means a greater EN difference and higher bond polarity.

Ranking Bond Polarity

  • For carbon bonds with halogens: C–I (EN diff 0.0), C–Br (0.3), C–Cl (0.5), C–F (1.5).
  • Order from least to most polar: C–I < C–Br < C–Cl < C–F.
  • For carbon's bonds: C–N (0.5) is most polar, C–H (0.4) is less polar, C–C (0.0) is nonpolar.

Key Terms & Definitions

  • Electronegativity — Measure of an atom’s ability to attract electrons in a bond.
  • Covalent Bond — Bond formed by the sharing of electrons between atoms.
  • Nonpolar Covalent Bond — Covalent bond with little or no EN difference (<0.5).
  • Polar Covalent Bond — Covalent bond with moderate EN difference (0.5–2.0).
  • Dipole Moment — Directional separation of charge in a polar bond, indicated by an arrow.

Action Items / Next Steps

  • Review electronegativity values for common elements.
  • Practice ranking bond polarity using EN differences or the periodic table.
  • Complete any assigned problems on bond polarity ranking.

Full transcript