What determines the energy level of an electron in an atom?

[sinjan.j]

My textbook says that, the energy level of an electron is decided by the pattern of charges surrounding it.

Can anybody explain how. Simple language please, I'm in 12th grade. Kindly provide example, if possible. Thank you.

 

[alxm]

Well, I can try. Bear in mind, the exact details of describing the state of an electron in an atom requires quantum mechanics (if you know a bit about the history here, you might know that describing electrons in atoms was in fact the physics problem that gave rise to QM in the first place).

Now, quantum mechanics dictates a couple of important things here: 1) The electrons in the atom can't be stationary; they must always be "in motion" 2) They can only occupy specific energy levels, which correspond to what you could consider 'stable patterns of motion', or in physics jargon 'stationary states' (meaning the state itself doesn't change over time, not that the electron is stationary). 3) Only two electrons can occupy any such state at a time.


Now in classical mechanics, a stable pattern of motion would be something like an orbit of a planet around a star. In quantum mechanics it doesn't work that way, because quantum objects don't have definite locations, and don't follow definite 'trajectories'. The state or what I called 'pattern of motion' doesn't actually look like a circular orbit. What you have instead is a pattern that tells you the probability of where you're likely to find the electron. We call that an 'orbital' (to distinguish it from a classical orbit). That pattern tells you what the charge density around the atom (coming from that electron) looks like.

Different energies of the electron mean it's occupying different orbitals, and so its charge density pattern around the atom looks different. They look like http://chemlinks.beloit.edu/Stars/images/orbitals.jpg" . Different energy states correspond directly to different charge distributions, because this charge distribution is basically a description of the electron's entire 'pattern of motion'.