The discovery of neutron was done by James Chadwick in 1932.
The neutron is a neutral particle found in the nucleus of an atom.
It is represented by symbol ‘n’.
Protons and neutrons are collectively known as nucleons.
Neutrons carry no charge.
Atoms of all the elements contain neutrons except ordinary hydrogen atom which does not contain ant neutron.
DISCOVERY OF NEUTRON
Rutherford discovered that except the hydrogen atom, the atomic mass of other elements could not be explained on the basis of only electrons and protons.
For instance, the atomic mass of a helium atom should be double that of a hydrogen atom. When the e/m ratio (charge to mass ratio) was calculated, it was discovered that the mass of helium ion was four times the mass of hydrogen atom.
So, Rutherford predicted the presence of a particle other than electrons and protons in an atom to explain this anomaly.
According to him such a particle should be electrically neutral and have the mass equal to that of a proton.
James Chadwick later confirmed the presence of neutrons from his experiment based on the interaction of alpha particles with beryllium.
CHARACTERISTICS OF NEUTRONS
Mass of neutron – The mass of a neutron is equal to that of a proton. Electrons are considered to have negligible mass, the mass of an electron is 1/1840 times that of the proton.
Thus, Mass of neutron = 1.676 x 10-27 kg = 1.676 x 10-24 g
The charge of a neutron – Neutrons do not carry any charge. Hence they are electrically neutral in nature.
DIFFERENCE BETWEEN VALENCY, A AND Z:
To find out the valency, electrons only in the outermost shell of the atom are considered.
But to determine the atomic number or the mass number, the total number of protons and neutrons are considered.
NOTATION OF ATOM:
An atom is represented in the following way
So, the notation of Carbon is:
CALCULATING NUMBER OF NEUTRONS:
The number of neutrons can be calculated by subtracting its atomic number from its mass number.