Numbers that specify the properties of atomic orbitals and of their electrons. They indicate the region occupied by a given orbital in terms of (1) distance from the nucleus, (2) orbital shape, and (3) orbital position for the three-dimensional x, y, and z axes.

Principal (n), angular (l), and magnetic (m) quantum numbers. The fourth is the spin quantum number (s).

Describes the size of the orbital and the distance from the nucleus. Orbitals for which n = 2 are larger than those for which n = 1. n values match the principal energy level: 1, 2, 3, 4, …

• PEL 1 → n = 1
• PEL 2 → n = 2
• PEL 3 → n = 3
• PEL 4 → n = 4

Describes the shape of the orbital (shape = sublevel). Allowed values run from 0 to (n − 1).

• s → l = 0
• p → l = 1
• d → l = 2
• f → l = 3

Indicates the orientation of an orbital about the nucleus. The number of m values equals the number of orbitals in the sublevel. Values of m range from −l to +l. Orbitals in a sublevel differ in orientation, not energy.

• s → m = 0
• p → m = −1, 0, +1
• d → m = −2, −1, 0, +1, +2
• f → m = −3, −2, −1, 0, +1, +2, +3

Indicates the spin of the electron. Can only have two possible values: +1/2 or −1/2. First electron in an orbital: s = +1/2. Second electron in an orbital: s = −1/2.

Each electron in an atom has its own set of 4 quantum numbers: PEL (n), sublevel (l), orbital (m), and spin (s).