The force that holds atoms and molecules together is the electrical force.

 

The force that holds the nucleus together is the strong force. The name of the force is “the strong force”. The strong force is like sticky glue. It acts only when the nucleons (protons or neutrons) touch.

 

One of the largest nucleons (protons and neutrons)  is the uranium nucleus. It has 238 nucleons. It has 92 protons. The protons want to get out, as each proton acts with a repulsive force on the others. Like charges repel. Since the strong force is stronger, the nucleus is held together. But just about. We cannot have a nucleus any larger, for then the protons indeed will repel.  Uranium 235 is even more unstable. If we fire a neutron on it, the extra energy will cause the protons to fly apart. Once they are apart, the strong force has no effect, as the strong force is a local (sticky) force.