Is HCN and SF6 polar or nonpolar?

Question

1.) How to get the electronegativity difference of HCN? (I am not sure how to get the EN difference of 3 elements in a compound).

2.) Is HCN polar or nonpolar?

3.) SF₆ has an EN difference of 1.5, right? So, is it polar or nonpolar?

Thank you in advance!

Answer 1

1. Differences in electronegativities are calculated for each bond in a molecule. For HCN you will calculate the difference between H and C which is 0.4 and the difference between C and N which is 0.5.
2. To determine if a molecule overall is polar or nonpolar you must look at both the electronegativity differences in each bond and the shape of the molecule. HCN is a linear molecule with a single bond between the H and the C and a triple bond between the C and the N. Looking at the electronegativities H<C<N (2.1<2.5<3.0). Carbon will pull the shared electrons in the H-C bond toward C and nitrogen will pull the shared electrons in the C-N triple bond toward N. This means that electrons are being pulled toward the nitrogen end of the molecule making that end of the molecule slightly negative. The hydrogen end of the molecule will be slightly positive because shared electrons are being pulled away from that end. Therefore, the molecule contains two polar bonds and is a polar molecule.
3. You are correct! Each S-F bond in the molecule does have a difference of 1.5. Therefore, each bond is polar. However, the shape of the molecule is called an Octahedron with 90 degree bond angles throughout making it a very symmetrical molecule. This symmetry means that even though each bond is polar these polar bonds are evenly distributed around the S atom making the overall molecule nonpolar. Think of it like a bizarre tug-of-war where 6 teams are pulling equally in 6 different, evenly-spaced directions. No one would ever win because their efforts would cancel each other out. When there is not a negative or positive side of a molecule it is nonpolar.

I hope this helped:)