So in any acid base reaction we have a hydrogen atom that is exchanged between our two molecules, the acid in the base. And at the same time, one Covalent bond is broken and another Covalent bond is actually formed. So let's suppose we have some hypothetical acid ha where A is simply an atom or a group of atoms that are attached to our H atom and this is a Covalent bond. Now, when this acid dissociates, this Covalent bond is broken and the two electrons in that Covalent bond end up on the A atom. And so this gains an additional electron and so it becomes an anion. It gains a negative charge while this one loses an electron.