Why are Metal Hydroxides Bases and Nonmetal Hydroxides Acids?
To understand why nonmetal hydroxides are acids and metal hydroxides are bases, we have to look at the electronegativities of the atoms in these compounds. Let’s start with a typical metal hydroxide: sodium hydroxide The difference between the electronegativities of sodium and oxygen is very large (EN = 2.5). As a result, the electrons in the NaO bond are not shared equally these electrons are drawn toward the more electronegative oxygen atom. NaOH therefore dissociates to give Na+ and OH- ions when it dissolves in water. We get a very different pattern when we apply the same procedure to hypochlorous acid, HOCl, a typical nonmetal hydroxide. Here, the difference between the electronegativities of the chlorine and oxygen atoms is small (EN = 0.28). As a result, the electrons in the ClO bond are shared more or less equally by the two atoms. The OH bond, on the other hand, is polar (EN = 1.24) the electrons in this bond are drawn toward the more electronegative oxygen atom. When this mol
