Principal Quantum Number (n)

This quantum number determines the main energy level or shell in which an electron is present. It is usually denoted by n and can have any whole number value such as: n = 1, 2, 3, 4 ….. etc. The various values of n as 1, 2, 3, 4 ….etc., are also called K, L, M, N etc. If n = 1, the energy level is closest to the nucleus and as the value of n increases, the distance of the energy level from the nucleus increases. This quantum number also determines the energy of the shell. For e.g., for hydrogen atom the energy is given by

where n is the principal quantum number. As the value of n increases, the electron gets farther away from the nucleus and its energy increases. Higher the value of n, higher is the electronic energy of the shell. Thus, principal quantum number gives the average distance of an electron from the nucleus and specifies the energy of that electron.