Ammonium, as a chemical species, does not have an atomic number. Atomic numbers are assigned to elements, which are defined by the number of protons in the nucleus of an atom. Ammonium (NH4+) is a polyatomic ion composed of one nitrogen atom (with atomic number 7) and four hydrogen atoms (with atomic number 1 each). The total charge of the ammonium ion is +1, indicating the loss of one electron from the nitrogen atom. However, it is important to note that ammonium is not considered an element but a charged ion derived from the element nitrogen.