Question

How does the interaction of polar covalent bonds allow hydrogen bonds to form?

Answer 1

When hydrogen is bound to a ..........

Explanation:

When hydrogen is bound to a strongly electronegative element, i.e. `O, N, F`, charge separation occurs as the heteroatom polarizes electron density from the bond to acquire a partially negative charge. And of course if the charge is partially negative, there must be a partial positive charge developed on the hydrogen.

And thus a molecular dipole is generated, and in the bulk solution the dipoles line up to given an extra, potent intermolecular force that is known as `"hydrogen bonding"`.

For hydrogen fluoride, we could represent this interaction as `stackrel(delta+)H-stackrel(delta-)F` `cdotsstackrel(delta+)H-stackrel(delta-)Fcdotsstackrel(delta+)H-`

And see this old answer.

And compare the boiling points of water, ammonia, and hydrogen fluoride with those of the lower group hydrides. The boiling points of these materials are absurdly high.