How do electrons gain energy and hop levels? Does it come from shooting it with a laser or introducing heat, or some such method? By the same token, why do electrons lose energy? I assume they don't say to themselves, "I'm feeling lazy" and move down a few levels.
Also, what is the energy called that they gain and lose? Is it "quantum" energy, radiation, EM energy, or some other type of energy?
An answer that is simpler would be best. Thanks!
If an electron is completely isolated then it can never change energy levels. So this means that when electrons change energy levels because of some interaction with an environment. A simple example is when one shoots em radiation at an electron.The interaction is accomplished by an exchange of a photon which is either emitted or absorbed. This emission or absorption of a photon in this case is what is seen as the changing of energy levels.One could also imagine interaction with a gravitational field(these would have to be strong because gravity is weak). In this case it is presumably exchange of a graviton.
So there is nothing mysterious, electrons or more generally quantum systems change energy levels because of interactions with other quantum systems. In these interactions there is exchange of energy as one would expect and this shows up as changing of energy levels.All this can be made precise but you asked for a simple answer.
You can think of an electron's energy level like a person on earth. You go up in elevation and you have more potential energy, go down in elevation and you release it. In this analogy, the higher energy level is the higher elevation.
With electrons, it is from getting hit by a photon. A photon is the particle that carries energy in the electromagnetic spectrum. This includes radio waves, heat, light, UV, and more. In order for the electron to change energy levels the photon it absorbs must carry at least enough energy for it to jump upwards
When people talk about atomic energy they usually mean nuclear power. You are talking about something else. Electrons bound to atoms have energy levels. They change from level to level as they gain and lose energy. This is quantum mechanics.
One of the problems with quantum mechanics is that it is so counter intuitive. It contradicts common sense. Questions of how and why it works cannot be answered in a satisfactory way. We can only say experiments have shown that it is a good description of the universe. The universe really does contradict common sense.
Richard Feynman gave one of the better explanations here. You can find the full set of lectures here.
