Question

Why is water unusual?

Answer 1

For such a small molecule, water has an exceptionally high boiling point, and this may be traced to the polarity of the `O-H` bond.

Explanation:

If you compare the boiling points of other small molecules, i.e. `NH_3`, `CH_4`, `H_2S`, to that of water, it is very clear that the `100` `""^@C` normal boiling point is exceptionally high. Because the oxygen hydrogen bond is polar, i.e. `""^(delta+)H-stackrel(delta-)O-H^(delta+)`water molecules engage in extensive intermolecular hydrogen bonding, and this substantially elevates the boiling point.