CoachA covalent bond between two atoms of different electronegativities is a polar bond: the shared pair sits closer to the more electronegative atom. That atom carries a small negative partial charge, written , and the other atom an equal positive partial charge, .
Examples
Example 30.7 (Four molecules)
Hydrogen chloride has one polar bond and is polar, chlorine . Ammonia , a pyramid of three polar bonds, is polar, nitrogen . Methane has only nearly non-polar bonds: non-polar. Tetrachloromethane has four polar bonds, but at the corners of a regular tetrahedron: their effects cancel and the molecule is non-polar.