Which molecule or compound below contains a POLAR covalent bond?

Question

a) C2H4

b) ZnS

c) LiI

d) NCl3

e) AgCl

I got b but a friend insists it's a. Who got this right? Or what's the correct answer? Please help. Thanks

Answer 1

a) C2H4 -- C-C bonds are nonpolar, C-H bonds are pretty much "not polar" since the DEN is only 0.35.

b) ZnS -- The DEN is 0.95, which is polar covalent

c) LiI -- DEN is 1.68 which is almost exactly a 50% ionic, 50% covalent bond.  I'd say pretty polar covalent

d) NCl3 - DEN is only 0.12 which is considered nonpolar

e) AgCl - DEN is 1.23, which is more covalent than ionic.  This would be polar covalent.

The ones that are polar covalent are

b, c, and e.

Don't be mislead by the notion that a metal-nonmetal compound is always ionic.  The difference in the electronegativies (DEN) must be 2.0 or greater to be considered ionic.

Answer 2

a is ethene. While there are covalent bonds, I wouldn't consider the bonds very polar at all.

b ZnS is ionic

c. LiI is ionic

d. I think this is the best answer. NCl3 is covalent and the lone pair of electrons on nitrogen give the molecule as a whole a diplole. Additionally, the N-CL bond is more polar then the C-H bond

e) AgCl is ionic