Number of protons = atomic number, assumed number of electrons = number of protons (all elements in the periodic table are assumed to have a neutral charge, in which case protons and electrons are equal in number. If this is not the case they will be ions of a certain element and wil have a + or - sign next to them.), number of neutrons= atomic wt - atomic number. Oxygen has an atomic number of 8 and an atomic wt of 16 so protons = 8, electrons = 8 and neutrons = 16-8, or 8
