The atomic number of
The number of protons is 7
The number of electrons is 7
The number of neutrons is 8
The atomic number of Nitrogen is 7 because Nitrogen has 7 protons.
The seven protons attract 7 electrons in the ground state.
If the atom had fewer or more than 7 protons the atom would not be Nitrogen.
The mass of the atom is the sum of protons and neutron. so