The nucleus is very small compared to the atom as a whole: as electrons are even smaller, most of an atom is empty space the diameter of a nucleus can be 100,000 times less than the diameter of an ...

Thus when an atom absorbs or gives off energy (as in light ... to the periodic repetition of properties of the elements. The shells in which electrons orbit have different quantum numbers and ...

Having a “magic” number of protons or neutrons means there are enough to fully occupy the nuclear valence shells (outermost orbits around the nucleus) in an atom and give it stability.