Energy level

Electrons can be arranged at different distances from the nucleus, called energy levels. An electron can move to a higher energy level, further from the nucleus, when the atom absorbs electromagnetic radiation. It can move to a lower energy level, closer to the nucleus, when the atom emits electromagnetic radiation.

Atoms and their nuclei cannot possess just any amount of internal energy. They have particular energy levels. An electron in an atom can occupy one of the atom’s allowed levels, while the nucleus has its own set of nuclear energy levels.

The electrons are arranged in energy levels at different distances from the nucleus. Levels closer to the nucleus have lower energy; levels further away have higher energy. An electron cannot settle at just any energy between these levels.