Electrons in atoms are arranged in energy levels (n), sublevels (l), and orbitals (ml). Quantum mechanics treats electrons as waves that can only gain or lose discrete amounts of energy called quanta when changing energy levels. Each energy level corresponds to a row on the periodic table and can contain one or more sublevels representing blocks. Sublevels include s, p, d and f orbitals which electrons fill according to specific rules. The electronic configuration notation specifies the distribution of electrons among the atomic orbitals.