- Electrons are present in all the atoms.

- Thomson proposed the plum-pudding model of the structure of atom.

- Rutherford’s model of the structure of atom suggested that most of the mass and all of positive charge of an atom is concentrated in its nucleus and the electrons revolve around it in.

- The neutrons are neutral particles present in the nucleus.

- Atomic number is the number of protons present in the nucleus of an atom.

- Mass number gives the number of protons and neutrons present in an atom

- Isotopes have same atomic number but different mass numbers.

- Bohr’s model gave the idea of definite orbits or stationary states.

- The electrons occupy various shells in an atom in the increasing order of their energy.
The maximum number of electrons which can be accommodated in a shell is 2n²