Question

Why do dipoles cancel out?

Answer 1

Well, not all of them do.....

Explanation:

Dipoles are vector quantities...and they have magnitude and direction, and are thus summed geometrically. The carbon dioxide molecule is definitely a species where there is charge separation between the carbon and the oxygen bonds....

`""^(-delta)O=stackrel(delta+)C=O^(delta-)`...but given the linear structure of this molecule `/_O-C-O=180^@`, the bond dipoles cancel out upon vector addition and to give a ZERO resultant, and `CO_2` is thus non-polar. For `""^(+delta)H-stackrel(delta-)O-H^(delta+)`, whose structure is bent, `/_H-O-H=104^@`, and the dipoles DO NOT geometrically sum to zero. Water is thus a polar molecule....