| number of protons in an atomic nucleus|
NOTE 1 The proton number is given by Z = A − N where A is the nucleon number and N the neutron number.
NOTE 2 The proton number gives the electric charge of the atomic nucleus in number of elementary electric charges.
NOTE 3 Atomic number is the order number of atom in the periodic chemical classification and relates to the chemical behaviour of the atom, i.e. its ability to produce combinations with other atoms. A chemical element consists of atoms having the same atomic number.