Dear Readers, Welcome to Awareness Adda. In the Previous article, we discussed The introduction of ChemistryPhysical ChemistryAtomic Mass and Mole concept and Atomic Structure today we will learn about Quantum Number. All these notes are very important to the examinations like SSC, RRB etc.. it is an important topic in chemistry. all these notes help you to get a good score in your examinations. Let’s go to the article.

           Before going to Quantum Number let’s learn about some concepts. they are shown below.

Shell or Orbit:

           The electrons revolve in various orbit with different and definite energies in the atom and these orbits which are the Trajectories or path the electrons are called shells.

           Various shells from lower to upper are represented symbolically by K.L, M, N, O, P etc..

Subshells or Sub-orbit:

           According to a 3d graphical plot of electric wave function any the internal atomic composition every shell or orbit these are represented by various small letters s, p, d, and f the maximum no of electrons in the orbitals p, d, and f are 2, 6, 10, 14 respectively. it is also observed hat in various shell K, L, M, N etc. subshells or sub-orbits s, sp, spd, spdf are respectively.


           An orbital is a 3d space around the nucleons of and atom where there is a maximum probability of finding an electron.

Electronic configuration:

           A comprehensive and proper distribution of the electrons in various shells and subshells of an atom is called electronic configuration.


Na(11)=    122,3.

Mg(12)=  122,3.

Ca(20)=  122,3,3,4.

           An electron occupies the orbital to lowest energy first and when it is filled up completely then remaining electrons are accommodated to the orbitals of the next higher energy.

           The order of filling of atomic orbitals with electrons can be shown as below.


 In above diagram 6f,6g, 6h,5f,5g electrons do not go to these orbits under normal condition.

           Thus according to Aufbau principle the order of energy is of various sub-shells. that is like in follows 1s<2s<2p<3s<4s<3d<4p<5s<4d<4d<5p<6s<4f<5d<6p<7d<7s<5f..

Quantum Number:

           The Quantum Number: The Quantum numbers are those are through which the position of electrons and their respective energies in various shells, sub-shells or orbitals are known to the position of an electron and its corresponding energy there are four parameters which are needed to describe it as below.

  • The orbit number in which electron exists.
  • The sub-orbit of the orbit in which electron resides.
  • The orbital of the sub-shell in which electron resides.
  • The electron which rotates in the orbital.

There are 4 quantum numbers.

  1. Principal Quantum Number.
  2. Azimuthal Quantum Number.
  3. Magnetic Quantum Number.
  4. Spin Quantum Number.

Principal Quantum number:

           The quantum number which simply indicates orbit number of an electron and its energy and it is represented by n=(1, 2, 3,…) where n is an integer for n=1, the electron is said to be in the normal state.

Azimuthal Quantum Number:

           The quantum number which represents the angular momentum which represents the angular momentum of the revolving electron and it is indicated by l. for principal quantum n, l has all the values from 0 to (n-1).


if n=1 then l=0,

if n=2 then l=0,1,

if n=3 then l=0, 1,2,

if n=4 then l=0, 1, 2, 3…. etc

Magnetic Quantum Number:

           Which indicates the direction of an orbit in space in a magnetic field and it is represented by m, the values of magnetic quantum number m depends on the value of 1 and its values are from-1 to +1 includes zero.


if l=0 then m=0, 

if l=1 then m=-1,0,+1,

Spin Quantum Number:

           It represents spin of the electron quantum mechanically it has been observed that electrons have two types of spin- clockwise(+1/2) anti-clockwise(-1/2) thus spin quantum number has two values +1/2 and -1.2 and represented by s.




Principal Quantum Number


Orbit number and the corresponding energy of the electron.

Azimuthal Quantum Number


Angular Momentum of the revolving electron of sub shell.

Magnetic Quantum Number


Direction of an orbital in the space of Magnetic field.

Spin Quantum number


Spin of the electron.

           In next article, we will provide notes about atomic structure. so keep in touch with us in Awareness Adda. these topics are very useful to you for getting a good score in your examinations and always remember that “The best preparation for tomorrow is doing your best today“. so prepare well All The Best. Thank you.