Hi, I just learned about oxidation and reduction reactions and I have some questions. Are all ionic reactions redox reactions? Do elements that make up covalent compounds always have an oxidation number of zero because they only share electrons, not give or take? That is what I was thinking, but according to my book, in the molecule H2S, H has an oxidation of +1 and S has one of -2, which doesn't make sense if its a covalent compound... Thanks.