In an atom, the electronic states are described by a series of quantum numbers: n, the Principal quantum number, l, the angular momentum quantum number, m, the magnetic quantum number, and the electron spin quantum number, m_s. The combination (n, l, m, m_s) defines the quantum state. A change in any one of these numbers signifies another distinct quantum state.

Restrictions are placed on the values that these numbers may have:
n = 1, 2, 3, 4, ......... to infinity
l = 0, 1, 2, 3, 4, ...... to (n -1)
m = -l, -(l -1), ......... , -1, 0, 1, ......... (l -1), l
m_s = + 1/2, -1/2