What are the forces that hold sodium and chloride ions together?

Sodium is a metal, Chloride is a non-metal.

Right off the bat, you know that in order for both of these atoms to achieve a full valence shell that the metal has to lose electrons, and the non-metal has to gain them.

Therefore, you have the transfer of electrons in this bond in order to form ions.

Na + and Cl-. This transfer of electrons in a bond is called an {{ Ionic Bond}}