Question

If you want a molecule that is highly polar, look for one that contains what chemical bond pairing?

Answer 1

Look for a bond between an atom of high electronegativity and an atom of moderate electronegativity.

Explanation:

I answer this from the perspective of a 2nd/3rd year undergraduate. Where there is a bond between an atom of high electronegativity and an atom of low electronegativity, we are likely to get charge transfer, and a resultant ionic bond.

On the other hand, in a bond between say carbon or silicon or hydrogen (moderate electronegativies) and atoms of high electronegativity, viz. fluorine, oxygen, or the halogens, the electronegative atom polarizes electron density towards itself, and polarizes the `"element'-element"` bond. We can represent such a bond dipole as `""^(delta+)C-X^(delta-)` or `""^(delta+)H-X^(delta-)`.

Such a description can rationalize observed reactivity at the electrophilic carbon centre. It can also help to rationalize the acidities of the hydrogen halides, `H-X`, which are clearly strong protic acids, yet are (or can be) molecular species.

We can also look at the solvents `H-F` and `OH_2`, where again the hydrogen atom is not overly electropositive, and a `H-X` bond dipole is maintained.

Confused yet? If you want clarification I will give it another go.