a grouping of electrons in an atom according to energy

A group of electrons which have a common energy level that forms part of the outer structure (shell) of an atom.

The orbitals around the nucleus of an atom where electrons reside. Also called electron orbitals and energy levels.

The grouping of electron orbits of similar, but distinct, energies in the atom.

An electron shell, also known as a main energy level, is a group of atomic orbitals with the same value of the principal quantum number n. Electron shells are made up of one or more electron subshells, or sublevels, which have two or more orbitals with the same angular momentum quantum number l. Electron shells make up the electron configuration of an atom.