why is a water molecule is much more likely to give up a proton than a methane molecule

The difference in acidity between a water molecule and a methane molecule can be explained by their chemical structures and the presence of functional groups.

Water (H2O) consists of two hydrogen atoms bonded to an oxygen atom. It has a bent shape, resulting in a polar molecule due to the electronegativity difference between oxygen and hydrogen. The oxygen atom is more electronegative and attracts electron density, leading to a partial negative charge (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms.

In contrast, methane (CH4) consists of a central carbon atom bonded to four hydrogen atoms. It is a tetrahedral molecule, and all the carbon-hydrogen bonds are nonpolar. This means that methane is a nonpolar molecule.

The difference in acidity between water and methane is mainly due to the presence of a lone pair of electrons on the oxygen atom in water. This lone pair can be easily donated to an acid, making water capable of acting as a proton (H+) donor or an acid.

When water donates a proton, it forms a hydronium ion (H3O+). This process is driven by the ability of the lone pair of electrons on the oxygen atom to stabilize the positive charge of the proton. In other words, water is an excellent proton donor because it can stabilize the resulting positive charge on its oxygen atom.

On the other hand, methane lacks a lone pair of electrons that can be easily donated. The carbon-hydrogen bonds are stronger and less polar compared to the oxygen-hydrogen bonds in water. Consequently, methane is much less likely to give up a proton and act as an acid compared to water.

In summary, the difference in acidity between water and methane can be attributed to the polar nature of water, the presence of a lone pair of electrons on the oxygen atom, and the ability of water to stabilize positive charges. Methane does not possess these characteristics, making it less likely to give up a proton and act as an acid.