Concept preview

What you will be able to do

1. 01Relate electronegativity difference to bond polarity
2. 02Explain how molecular shape decides whether a molecule is polar
3. 03Describe dipole-dipole forces and hydrogen bonding

In a covalent bond two atoms share a pair of electrons, but they rarely share equally. The more electronegative atom pulls the shared electrons closer to itself. The larger the difference in electronegativity, the more one-sided the sharing. When two identical atoms bond (as in $\mathrm{Cl_2}$) the sharing is perfectly even; when very different atoms bond (as in HF) it is strongly lopsided.