chemistry help please!?

Question

Consider the following molecules:

A) SF6
B) F2
C) SF4
D) PF3
E) CF4


Which one of these molecules has bonds that are most polar?
Which have a molecular dipole moment?

Answer 1

The molecule with the most polar bonds is PF3, because it has the greatest electronegativity difference. (P is 2.1, S and C are both 2.5 vs. F at 4.0).

As for dipole moments, only PF3 has a dipole, as the lone pair of electrons on the phosphorus makes the molecule pyramidal and the vector sum of the individual bond dipoles cannot cancel. SF6 is octahedral, so all of the dipoles cancel. F2 is non-polar. SF4 has two lone pairs on the sulfur, but since it starts from the octahedral electronic geometry, those lone pairs are as far apart as possible, making the molecular geometry square planar, and all of the dipoles cancel. CF4 is tetrahedral, and the dipoles cancel as well.

Answer 2

You need to look at an electronegativity chart. Then subtract electronegativities.

Answer 3

PF3, it's the only polar one there.