The principal quantum number is the first in a set of four quantum numbers used in quantum mechanics to describe atomic orbitals, or the arrangement of electrons around a nucleus. The principal quantum number represents the overall energy level of the orbital and is often called the "shell." It is denoted with the symbol "n" and is always valued with a positive integer (n=1, 2, 3, etc.). In general, the higher the n value means the higher the energy level of the electron and the more likely it is to be located further from the nucleus. As an example, when the electronic configuration of the single electron in a hydrogen atom is written as 1s^1, the first "1" denotes the principal quantum number of the electron (in other words it is in the first atomic shell).
All electrons in an atom can be uniquely described by a set of four quantum numbers. This follows from Pauli’s Exclusion Principle.
The principle quantum number or n is indicative of the energy level of the electron. As an electron gains more energy it moves farther away from the nucleus and has a higher value of n. The value of n starts from 1, which denotes the set of electrons closest to the nucleus and as n increases it represents the set of electrons lying farther away from the nucleus.
The number of electrons that can have a particular value of n is given by 2*n^2. So the number of electrons with n= 1, 2, 3 and 4 is 2, 8, 18 and 32.
When an atom reacts with another atom, it is the electrons with the highest value of n that take part in the reaction.
Principle Quantum Number is the first of the the Quantum numbers of the atomic orbital system. The Principle Quantum Number is indicated by the letter 'n' and is always an intergral number i.e `ninZZ`
The Principle Quantum Number indicates the energy level in which the elelctron is present. It was first described in Bohr's atomic model. The value of n stars from 1 and increases by one for every increase in energy level. Electrons in higher energy orbitals are more loosely bound to the nucleus as compared to the electrons in the lower energy orbital.
Thus, the principle quantum number indicates the energy level of the orbital that the electron is associated with.