Answers (3)
An electron is a negatively charged subatomic particle. It can be either free , or bound to the nucleus of an atom. Electrons in atoms exist in spherical shells of various radii, representing energy levels. The larger the spherical shell, the higher the energy contained in the electron.
here's an explanation for kids, that can always be helpful:
http://www.historyforkids.org/scienceforkids/chemistry/atoms/electron.htm
:)