DISCOVERY OF NEUTRON IN FULL DETAILS


After the discovery of protons and electrons, it was noticed that all the mass of an atoms cannot be accounted for on the basis of only protons and electrons presents in it.
For example, a carbon atom contains 6 protons and 6 electrons. Now, the mass of electrons is so small that it can be ignored. So, the atomic mass of carbon  should be only
6u.This, however ,is wrong because the actual atomic mass of carbon is 12u. Then , how do we explain this extra mass of 6 units ? This problem was solved by the discovery 
of another subatomic particle by James Chadwick in 1932. This particle is called neutron. The neutron is a neutral particle found in the nucleus of an atom. Atoms of all
the elements contain neutrons except ordinary hydrogen atom which does not contain any neutron . Thus, the subatomic particle not presents in a hydrogen atom is neutron 
A hydrogen atom contains only one proton and one electron. A neutron is represented by the symbol n.


characteristics of a neutron.

1. Mass of a Neutron.
  The mass of a neutron is equal to the mass of a proton. In other words, the relative mass of a neutron is 1 u . The absolute mass of a neutron is 1.6*10^-24 gram.

2. Charge of a Neutron.
The neutron has no charge., It is electrically neutral.
We are now in a position to explain why the atomic mass of carbon is 12u. It is now known that  carbon atom contain 6 protons and 6 neutrons , each having a mass of 1u . Now,
  atomic mass of carbon= mass of 6 protons+ mass of 6 neutrons
                                          =6*1 +6*1
                                            =  12 u

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