Atomic Number

This gives the number of protons or electrons required in the atom for each element. For the hydrogen atom in Fig. 1, the atomic number is 1, which means the nucleus has 1 proton balanced by 1 orbital electrons. Similarly, the carbon atom in Fig. 2 with atomic number 6 has 6 protons in the nucleus and 6 orbital electrons. Also, the copper atom has 29 electrons because its atomic number is 29.