Polar and Nonpolar Molecules

[705960769]

Can someone explain why we can use symmetry in order to determine if a molecule is polar or nonpolar?

[505934309]

We use symmetry to determine polarity because the dipole moments can cancel each other out if they are across from each other, leading to a net dipole moment of zero.

[Brian Kim 1L]

Hello, I believe the symmetry of a molecule can help determine polarity because if the molecule is polar, there will be no net dipole moment even if the bonds within the molecule are polar. If the dipole moments within the molecule cancel out, the molecule will overall be nonpolar.

[Katie L 2I]

To give you an example, I think that Achieve question #7 is a great example, comparing between SO2 and CO2. As others already said, if the dipole moments, regardless if it's a polar or nonpolar bond, cancel each other out, the molecule will be nonpolar. From the Lewis structures of the two molecules, O is a highly electronegative molecule, so it will have a negative pull towards it.
What makes SO2 polar and CO2 nonpolar is the symmetry. Because of the lone pair on S making the molecule bent, the dipole moments still go towards the oxygen, but downwards diagonally, not cancelling one another out. CO2 is linear, so the dipole moments towards its oxygens are symmetrical and going in opposite directions from one another, cancelling each other out = nonpolar. Despite having polar bonds between C and O, the cancelling makes the molecule nonpolar.

[Isaac 14B]

We consider the physical mechanics of molecules when we look at symmetry as counteracting forces will indeed cancel each other out, leading to changes in polarity labelling. If we have a completely linear molecule with two directional polar tendencies, they will indeed cancel out and deem the molecule nonpolar. The use of symmetry to determine if molecules are polar or nonpolar is based on the idea that symmetrically arranged charge distributions cancel each other out, leading to a nonpolar molecule. On the other hand, if the charge distribution is asymmetrical, it results in a polar molecule.