The quantum number that describes the size, and therefore the relative energy, of an orbital.

() The quantum number that determines the size and (in hydrogen atoms) the energy of an orbital. n is used to label electron shells. n may take on integer values from 1 to infinity.

The number related to the amount of energy an electron has and therefore describing which shell the electron is in.

labels an electron's orbit and the allowed energy for the electron (see figure 27.13)

In atomic physics, the principal quantum number symbolized as n is the first of a set of quantum numbers (which includes: the principal quantum number, the azimuthal quantum number, the magnetic quantum number, and the spin quantum number) of an atomic orbital. The quantum number n labels the energy levels of the hydrogen-like atom. It is the first in a set of numbers that show the unique quantum state of an electron.