The number of protons in a nucleus is called the atomic number, and the number of electrons in orbit around the nucleus is usually equal. Both atoms that have the same number of protons-the atomic number-are also atoms of the same element.
Atomic Number, also expressed by the symbol Z, the number of protons in the nucleus of the molecule, and number of electrons in the neutral atom. Atoms with the same number of atoms represent a chemical element. In 1913 H. G. J. Moseley allocated atomic numbers to the elements for the first time. He grouped the elements in an order dependent on some of their X-ray spectra characteristics and then numbered them accordingly. The elements are all grouped to the order of their atomic numbers in the periodic table. The periodic law of Mendeleev was initially based on atomic weights.