Atomic number or Nuclear charge
(i) The number of protons present in the nucleus of the atom is called atomic number (Z).
(ii) It was determined by Moseley as, √v = a (Z-b) or aZ-ab
Where, v = X- ray’s frequency Z = atomic number of the metal a& b are constant.
(iii) Atomic number = Number of positive charge on nucleus = Number of protons in nucleus = Number of electrons in neutral atom.
(iv) Two different elements can never have identical atomic number.