Question

If NH3, HF and H20 all have H-bonding, why is H2O's boiling point(100) higher than HF(19.5) and NH3(-33)?

Answer 1

Both HF and NH3 can H-bond once per molecule, but H2O can H-bond twice per molecule.

Answer 2

how once ? when NH3 has 3 bonds?

Answer 3

NH3 has only one lone pair.to help attract a neighboring hydrogen. that's the definition of H-bonding

Answer 4

Thanks JFraser

Answer 5

Hi JFraser, thx for the answer. Since H-bonding is the bond formed between the lone pair of a F,N,O atom, HF can form 3 H-bonds, but why is its bp still lower than H2O which form 2 H-bonds ?

Answer 6

the H-F bond is more polar than the H-O bond in water or the H-N bond in ammonia. HF doesn't attract other hydrogens as strongly because its bond is too polar.