Another name for the principal quantum number is the shell number. It is essentially the same concept as the n in the Bohr atom description. The principal quantum number defines the location of the energy level. This number, n, is referred to as the principal quantum number. Generally speaking, the energy of an electron in an atom is greater for greater values of n. The energy levels are labeled with an n value, where n = 1, 2, 3, etc. It is said that the energy of an electron in an atom is quantized that is, it can be equal only to certain specific values and can jump from one energy level to another but not transition smoothly or stay between these levels. The two possible spinning motions for the electron are clockwise, indicated by an m s of +1/2, and counterclockwise, indicated by an m s of –1/2. Electrons are spinning charges and behave like tiny bar magnets. The fourth quantum number, m s, is the spin quantum number. The 2 p subshell has three 2 p orbitals, as there are three values for m l, –1, 0, and +1. These are the 2 s and 2 p subshells, respectively. When n is two, there are two subshells, as l can be zero or one. The number of orientations for a given subshell is equal to 2 l + 1.

m l can have any integer value between – l and + l, including zero. The magnetic quantum number, m l, describes the orientation in space of the orbital that the electron occupies, which is also related to the electron’s angular momentum. These will be discussed in the next lesson. Zero, one, two, and three correspond to s, p, d, and f orbitals, respectively. Subshells are designated by letters associated with the values of l. The number of possible l values indicates the number of groups of differently shaped orbitals, or subshells, at the nth energy level. When n is three, l can be zero, one, or two. When n is two, l has two possible values - zero and one. L can have integer values from 0 to n – 1 for each value of n. The angular momentum, or azimuthal, quantum number, l, describes the shape of the orbital that the electron occupies, which is related to the electron’s angular momentum. The greater the value of n, the farther the electron is from the nucleus.

n can have integer values of one, two, three, and so forth. The principal quantum number, n, denotes the energy level to which an electron belongs. These three quantum numbers define where in space the electron is most likely to be located. Each electron is described by four quantum numbers, three of which have interrelated values.

Quantum numbers