What is principal quantum number

In chemistry, this quantum number is very important since it specifies the shape of an atomic orbital and strongly influences chemical bonds and bond angles. The magnetic quantum number describes the energy levels available within a subshell and yields the projection of the orbital angular momentum along a specified axis.

The fourth quantum number describes the spin intrinsic angular momentum of the electron within that orbital and gives the projection of the spin angular momentum s along the specified axis. Each electron in any individual orbital must have different spins because of the Pauli exclusion principle, therefore an orbital never contains more than two electrons.

For example, the quantum numbers of electrons from a magnesium atom are listed below. Remember that each list of numbers corresponds to n , l , m l , m s. Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. The number of angular nodes is equal to the value of l , so the number of nodes is also 4. Electron Spin.

The fourth quantum number is independent of the first three, allowing the first three quantum numbers of two electrons to be the same. The value of the principal quantum number n is the level of the principal electronic shell principal level. All orbitals that have the same n value are in the same principal level.

When the value of n is higher, the number of principal electronic shells is greater. This causes a greater distance between the farthest electron and the nucleus.

As a result, the size of the atom and its atomic radius increases. Because the atomic radius increases, the electrons are farther from the nucleus. Thus it is easier for the atom to expel an electron because the nucleus does not have as strong a pull on it, and the ionization energy decreases.

The number of values of the orbital angular number l can also be used to identify the number of subshells in a principal electron shell:. After looking at the examples above, we see that the value of n is equal to the number of subshells in a principal electronic shell:. To identify what type of possible subshells n has, these subshells have been assigned letter names. The value of l determines the name of the subshell:. We can designate a principal quantum number, n, and a certain subshell by combining the value of n and the name of the subshell which can be found using l.

Knowing that the principal quantum number n is 4 and using the table above, we can conclude that it is 4p. The number of orbitals in a subshell is equivalent to the number of values the magnetic quantum number ml takes on. This equation will not give you the value of ml, but the number of possible values that ml can take on in a particular orbital. The names of the orbitals are named after the subshells they are found in:. In the figure below, we see examples of two orbitals: the p orbital blue and the s orbital red.

The inner, core electrons inner shell do not usually play a role in chemical bonding. Elements with similar properties generally have similar outer shell configurations.

The next shell down is now the outermost shell, which is now full — meaning there is very little tendency to gain or lose more electrons. The ion's electron configuration is the same as the nearest noble gas — the ion is said to be isoelectronic with the nearest noble gas.

Atoms "prefer" to have a filled outermost shell because this is more electronically stable. Martin S. Updated November 06, Featured Video. Cite this Article Format. Helmenstine, Anne Marie, Ph. Principal Quantum Number Definition. Quantum Numbers and Electron Orbitals.

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