The second column is the azimuthal quantum number of the subshell.

A subshell is the set of states defined by a common azimuthal quantum number, ℓ, within a shell.

The azimuthal quantum number represents the orbital angular momentum of an electron around its nucleus.

The azimuthal quantum number arose in the solution of the polar part of the wave equation as shown below.

In an s orbital, no nodes go through the nucleus, therefore the corresponding azimuthal quantum number ℓ takes the value of 0.

The azimuthal quantum number was carried over from the Bohr model of the atom, and was posited by Arnold Sommerfeld.

He introduced the 2nd quantum number (azimuthal quantum number) and the 4th quantum number (spin quantum number).

The azimuthal quantum number is a quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital.

For the hydrogen atom, , , and where is the Bohr Radius, is the principal quantum number and is the azimuthal quantum number.

In terms of atomic quantum numbers, each row corresponds to one value of the sum (n+l) where n is the principal quantum number and l the azimuthal quantum number.

In such cases, the orbital types (determined by the azimuthal quantum number l) as well as their levels within the molecule affect Z and therefore also affect the various atomic electron energy levels.

This includes i) electrons with a smaller principal quantum number and ii) electrons with an equal principal quantum number and a smaller azimuthal quantum number (l)

The ability of an element to catenate is primarily based on the bond energy of the element to itself, which decreases with more diffuse orbitals (those with higher azimuthal quantum number) overlapping to form the bond.

There is another quantity of angular momentum, called the orbital angular momentum, (azimuthal quantum number L), that comes in increments of 1 ħ, which represent the angular moment due to quarks orbiting around each other.

Firstly, the electrons are arranged into a sequence of groups in order of increasing principal quantum number n, and for equal n in order of increasing azimuthal quantum number l, except that s- and p- orbitals are kept together.

This formula is not correct in quantum mechanics as the angular momentum magnitude is described by the azimuthal quantum number, but the energy levels are accurate and classically they correspond to the sum of potential and kinetic energy of the electron.

The azimuthal quantum number is the second of a set of quantum numbers which describe the unique quantum state of an electron (the others being the principal quantum number, following spectroscopic notation, the magnetic quantum number, and the spin quantum number).

These letters were later associated with the azimuthal quantum number, l. The letters, "s", "p", "d", and "f", for the first four values of l were chosen to be the first letters of properties of the spectral series observed in alkali metals.

The choice of letters originates from a now-obsolete system of categorizing spectral lines as "sharp", "principal", "diffuse" and "fundamental" (or "fine"), based on their observed fine structure: their modern usage indicates orbitals with an azimuthal quantum number, l, of 0, 1, 2 or 3 respectively.

It is, however, possible to simultaneously measure or specify L and any one component of L; for example, L and L. This is often useful, and the values are characterized by azimuthal quantum number and magnetic quantum number, as discussed further below.