Atoms can gain lose or share electrons durning a chemical change why doesn't this cause the atoms identities to change?

An atom's identity, that is, whether it is 'oxygen' or 'plutonium', for example, is determined solely by the number of protons in the nucleus. The number of neutrons also plays a part - a differing number of neutrons can change an atom from one isotope of an element into another, but the atoms would still remain the same element, albeit a different isotope. The number of electrons orbiting the atom does not change the identity of the atom, only it's electronic state. Take electrons away and it becomes a positively charged ion of the same element. Add electrons and it becomes a negatively charged ion, but still of the same element.