Question

Why would a molecule such as methane not dissolve well into water?

Answer 1

Well, methane is a non-polar molecule. These nonpolar molecules don't dissolve so well in water. You may have heard `"like dissolves like"`, since water is polar, it naturally tends to dissolve with other polar molecules.

Explanation:

Well, methane is a non-polar molecule that contains relatively non-polar `C-H` bonds. The `C-H` bond has negligible dipole moment, and even if it did have some polarity, the tetrahedral shape of the molecule would give no net dipole. Compare the solubility of `"CCl"_4` in water which is also poor.

As chemists, as physical scientists, however, we should always seek out the data to inform our argument. This site quotes a solubility of `0.04*g*kg^-1"(of water)"`, which is comparable to the solubility of the dinitrogen molecule under equivalent conditions.