The original theory of electrons was based on the Newtonian planetary model that the electrons spun around the nucelus of the atom much like the planets spinning around the Sun in our solar system.

If positive and negative charges attract, it was wondered why the electrons don’t crash into the protons in the nucleus.

Niels Bohr solved this problem by determining that the amount of energy has is the determinism of how far it is from the nucleus.

Electrons have been likened to a person on a stair case, only being able to exist on one step on a stairwell at a time, and only being able to go one step at a time.