Question

Why is that, in terms of electronegativity, a `C-O` bond in `CO_2` is more polar than the `F-F` bond in `F_2`?

Answer 1

Because all isotopic fluorines of the same kind (e.g. `""^19 "F"`) are identical. The electronegativity of fluorine is equal to itself, therefore the electronegativity difference is `0`.

The electronegativity of carbon is about `2.5`, and that of oxygen is about `3.5`, and naturally, `(3.5 - 2.5 = 1.0) > 0`. So, the electronegativity difference is greater for a `"C"-"O"` single bond than a `"F"-"F"` single bond.