Quantum Numbers:What are Quantum Numbers in Chemistry and  How to Find Quantum numbers?

● In an atom, the electrons are arranged in different energy levels.These electrons not only rotate around the nucleus but also rotate around their own axes.


According to the quantum mechanics, three interrelated numbers are required to express the size, shape and orientation of the orbitals of electrons in an atom.

Moreover, there is a number to express the direction of spin of the electron. These four corelated numbers are called quantum numbers which are as follows:

1. Principal quantum number, n

2. Azimuthal or subsidiary quantum number,l

3. Magnetic quantum number, m

4. Spin quantum number, s


●Question:How many quantum numbers are there?

Ans:There are four quantum numbers.

1)Principal Quantum Number:How to Find Principal Quantum number

The quantum number that expresses the main energy

level in which the electrons are moving around the nucleus is the principal quantum number.


Principal quantum number is expressed by n, where n= 1, 2, 3, 4 etc. It also represents the average distance of the
electron's orbit from the nucleus. 


As the value of n increases, the distance of the orbit from
the nucleus, ie. the size of the orbit increases. 

Bohr gave the idea of this quantum number.
When n=1,2,3,4,5 etc. the energy levels are known as K, L, M, N ,O shell respectively. 

The maximum number of clectrons which can rotate in each particular orbit is given by 2n².

Different Orbits or Shells and Their Accommodated Electrons

2)Azimuthal or Subsidiary Quantum Number,l:How to Find or Calculate Azimuthal Quantum Number