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.