<Dl> <Dd> L = n ⋅ ħ = n ⋅ h 2 π (\ displaystyle \ mathbf (L) = n \ cdot \ hbar = n \ cdot (h \ over 2 \ pi)) </Dd> </Dl> <Dd> L = n ⋅ ħ = n ⋅ h 2 π (\ displaystyle \ mathbf (L) = n \ cdot \ hbar = n \ cdot (h \ over 2 \ pi)) </Dd> <P> where n = 1, 2, 3,...and is called the principal quantum number, and h is Planck's constant . 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 . </P> <P> The principal quantum number n represents the relative overall energy of each orbital, and the energy of each orbital increases as the distance from the nucleus increases . The sets of orbitals with the same n value are often referred to as electron shells or energy levels . </P>

Principal quantum number of an atom is related to