Net nuclear spin

Net nuclear spin can be looked at the same way as electrons are in molecular orbital theory. An atom of chlorine has 17 electrons, so one would think that it would have a charge of -17, but it also has 17 protons with 17 positive charges so the net charge is 0, even though the negatives are from tiny electrons while the positives are from much larger protons. Adding one extra electron to the atom turns it into an ion with a net charge of -1.

Similarly, for a simple nucleus which is composed of spin 1/2 protons and neutrons, 2 protons and 2 neutrons pair up, negating their spins. Any extra, lone spins would determine the net spin of the nucleus. However, complications arise to due other quantum properties of neutrons and protons that make things more difficult as the nucleus gets bigger. Thus nuclear spins must be measured, not calculated.