Discovery of Neutrons

Discovery of neutron

It was discovered by Chadwick in the year 1932. It was actually discovered while considering the mass of atomic particles. It was seen that the whole mass of an atom is due to the nucleus and as far we know, the nucleus is positively charged. That means it has only protons in it. But we also know that the mass of an atom is never equal to the number of protons. This shows that the nucleus contains some other particles also that contribute towards mass only and not towards charge. Therefore, the particles were called neutrons (as they possess no charge).

Bohr’s theory

To overcome the limitations of Rutherford model, the new concept and picture of atom was given by Neil Bohr which made a great contribution in knowing the structure of an atom. According to it:

  • Atom is electrically neutral i.e. number of Protons = number of Electrons.
  • In the centre of an atom, nucleus is present which is positively charged.
  • In the nucleus, protons and neutrons are present.

Protons possess = positive

Neutron possess = no charge

  • Outside the nucleus, shells or energy levels designated as K,L,M,N and so on  are present.
  • In shells, electrons revolve.
  • Electrons are negatively charged.
  • Each shell has a fixed amount of energy. So, as long as an electron remains in the same shell, it never loses or gains energy.
  • Number of electrons  in each shell is determined by Bohr Bury rule i.e. 2n2.