Electrons are found in parts of an atom called shells that cover different energy levels and are referred to by the letters K, L, M, N, O, P and Q.
The K shell has the lowest energy level in an atom, while the Q shell has the highest. Each shell can only hold a certain maximum number of electrons. Within each shell, electrons are located in subshells or suborbitals. These subshells are named by the letters s, p, d, f, g and h. As with the main shells, the subshells are also limited in the number of electrons each can contain.