Why are the normal boiling points of #HF#, and #H_2O# so high?

1 Answer
anor277
Apr 22, 2017

Well, let's look at some figures first...........

Explanation:

#"Normal boiling point of water"=100# #""^@C.#

#"Normal boiling point of HF"=19.5# #""^@C.#

Now, the volatility of each solvent reflects the degree of intermolecular force, and hydrogen bonding operates in BOTH solvents as the dominant intermolecular force. So why the discrepancy?

If you look at a text, I would be surprised if you find a definitive, and comprehensive answer (certainly you will not get one from me!). Both molecules are small, and certainly in comparison to the homologous hydrides, these boiling points are high.

As far as I know, the best reason that I can advance is that the water can form 4 intermolecular bonds per molecule while #"HF"# can only form the 2. Intermolecular bonding in water also extends in 3-dimensions, whereas it is 2-dimensional in hydrogen fluoride.

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