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 thann. 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.