There are special limitations on the values of n, l, and m that an electron in an atom can have. As with the Bohr theory for the hydrogen atom, n only can be a positive integer:

n = 1, 2, 3, 4, 5, 6, 7, - -

Quantum number I can be zero or any positive integer less than n. States with I = 0, 1, 2, 3, 4, 5, 6 . . .are identified by the lower case letters s, p, d, f, g, h, i . . . respectively. A state with n = 3 and I = 2 is called a 3d state. The possible n and I combinations for n = 1 through 4 are shown in the table at the top of the next page.

The magnetic quantum number, m, can have any integral value from -I to +l, including zero. These values are less important at the moment than are the number of such m states that exist. For each I value there are exactly (2l + 1) different m states, as shown in the table opposite.