Dear Readers, Welcome to Awareness Adda. In the Previous article, we discussed the introduction of Chemistry, Physical Chemistry and Atomic Mass and Mole concept.  today we will learn about Atomic Structure. 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.


           In 1803 John Dalton propounded the atomic theory according to which an atom is indivisible and this concept was prevalent up to 19th century. The atomic model is like Rutherford’s model, Bohr’s model, Vector’s model. these microparticles are called elementary particles or fundamental particles.

Atomic and molecule: 

           The atom of an element is the smallest particle which takes part in a chemical reaction but does not exist in a free state in nature.

Main Fundamental particles of the atom:


           It was invented by J.J.Thomson in 1897 and it is a negatively charged particle which rotates in various orbits around the nucleus. the mass of an electron 9.1xkg. and  the charge of an electron is -1.6xcoulomb. 


           It was invented by Gold stein in 1919 and it is a positively charged stable particle. the mass of an proton is 1.67xkg. and charge of a proton is +1.6xcoulomb. 


           It was invented by Chadwick in 1932. which is neutron unstable particle. the masses of a proton and neutron are equal.

Rutherford’s Atomic model:

           In 1911 Rutherford conducted an experiment to detect the inner composition of an atom and it is called Rutherford’s ∝-scattering experiment.

this model has the following conclusions:

  • In an atom, there is a central massive part and it is called nucleus which is surrounded by the electrons and in this nucleus proton and neutron are packed together.
  • The atom is spherical and most of this part is empty.
  • The size of the nucleus is very small in comparison to entire atom.

Bohr’s Atomic model:

           In 1913 Neils Bohr introduced a revolutionary concept to explain the stability of an atom. he asserted that its old classical laws which are applicable to macro bodies cannot be directly applied to the sub-atomic particles like electrons and protons.

Bohr gave the following new ideas on the basis of plank’s quantum theory which is called the postulates of Bohr’s theory and these are given as below.

  • The centripetal force required for an orbital electron is counted on balanced by the electro-statical Colombian force of attraction between the nucleus and the electron.
  • The electron in an atom only revolves in a certain definite orbit in which energy is fixed and quantised.

The angular momentum of such orbits must be quantized which is equal to an integral multiple of h/2π. 

Atomic number:

           The no.of protons and electrons of an atom of the element of an atom of the element os called an atomic number of the element and it is represented by’z’. obviously, the nucleons of the hydrogen atom have 1 proton and 1 electron exists, that’s why hydrogen atom is said to have 1 atomic number. 

Mass number: 

           In energy atom, there is a small center as massive part called nucleons.  the nucleus of an atom consists of proton and neutron which is collectively called nucleus. the sum of the number of protons and neutrons of the nucleolus of an atom of the element os called mass number and it is represented by A.

Atomic symbol of an element: 

           An atom x of an element can be represented by an atomic symbol given as below.

 where z=Atomic number,

where the z=Atomic number,

           A=Mass number.

           These are the short notes on Atomic Structure. we will provide some important notes on next article so keep in touch with Awareness Adda. if you have any droughts or suggestions gave us in the comments section.  if you want to go previous articles you can just click on the links.  But always remember that “The best preparation for tomorrow is doing your best today“. All The Best.Thank you..!