Question

Why is a compound as common as water considered a "weird" chemical substance?

Answer 1

Hydrogen bonds

Explanation:

Water contains hydrogen bonds between the molecules which means that it will remain as a liquid at much higher temperatures than you would expect. This also enables the molecules to 'stick' together and gives water surface tension. The way that water forms into a solid also means that the solid of water (ice) is much less dense than the liquid, allowing it to float.

Answer 2

Consider its normal boiling point, which you know........

Explanation:

Compare the normal boiling point of water to that of `CH_4`, `SiH_4`, `HF`, `H_2S`, or `PH_3`. The boiling point of water is disproportionately high. This is also unusual in that water has a very small molecular mass (and thus little possibility of `"van der Waals interactions"`.

And now compare the density of liquid water to the density of solid water. Icebergs float in the ocean! I grant that things are more buoyant in salty water, however, ice cubes also float in ice-water or in your gin and tonic. This is highly unusual, in that, save water, there are very few substances that as liquids are DENSER than their solid phases.

I would consult a textbook on the unusual properties of water. These properties are largely the result of the propensity of the water to `"hydrogen-bond"` intermolecularly.