I don't know much about chemistry but trying to learn a few things to get better at geology. I am confused about SiO4. I know a silicon atom has 4 electron at the outermost shell. If it interacts with oxygen atoms in this case 4 of them it loses electron and oxygen atom gains electron. Since the silicon atom's charge is 4 in a SiO4 tetrahedron it means it loses 4 electron and this leads me to think it gives 1 electron to every oxygen atom in the bond which makes oxygen atoms' charge -1. I think the total charge of bond would be -4 due to 4 * -1 = -4 but the book I have says it is -8 meaning each oxygen atom has electric charge of -2. Can you help me to understand why it is -8 and not -4? Thanks.