Question

P.S./Chem.–Aug. ’15 40 Which statement explains why a C–O bond is more polar than a F–O bond?

According to the answer, "The difference in electronegativity between
carbon and oxygen is greater than that
between fluorine and oxygen."
But why? Fluorine has an Electronegativity of 4.0, while carbon has an electronegativity of 2.6.
So shouldn't F-O bond be more polar than C-O bond?

Answer 1

The difference in electronegativity is the key.

Explanation:

Keep in mind that you must compare carbon's electronegativity with that of oxygen, not with that of fluorine.

The `"C"-"O"` bond is more polar than the `"F"-"O"` bond because the difference between the electronegativity of fluorine and that of oxygen is smaller than the difference between the electronegativity of carbon and that of oxygen.

In the `"C"-"O"` bond, oxygen is the more electronegative element by a difference of

`Delta_"E.N." = 3.44 - 2.55 = 0.89`

In the `"F"-"O"` bond, oxygen is the less electronegative element by a difference of

`Delta_"E.N." = 3.98 - 3.44 = 0.54`

Because the difference in electronegativity, `Delta_"E.N."` is greater for the `"C"-"O"` bond, that bond will be more polar.

What this means is that when oxygen is bonded to carbon, oxygen will polarize the bonding electrons towards it by a greater extent than fluorine will do so when fluorine is bonded to oxygen.