DISCOVERY OF PROTON:
IT WAS DONE BY E. GOLDSTEIN
- In 1836 the same experiment was carried out where the same conditions were provided. The gas at low pressure was taken and current was passed.
- The high voltage between the electrodes was passed. It was found that when cathode rays passed through the gas, they ionized the gas by taking electrons along, leaving behind positively ionized gas particles.
- These particles were travelling towards cathode.These particles were found to form the beam of rays of positively charged particles and were called as canal rays.
- These rays consist of positively charged particles called a proton.
Properties of anode rays
- They also travel in straight line.
- They are also made up of particles.
- They carry positive charge.
- Their ratio of charge to mass was different for different gas that was taken in tube.
- The mass of particles were found to be different for different gases. It was nearly equal to the mass of atom.
When hydrogen gas was taken in the tube its mass was found to be minimum. As we know, Hydrogen atom is the lightest one and its charge to be same as Electron. It is 1.6×10-19C and its e/m ratio taken as standard that is 1.67x 10-24g.
Proton is defined as a
“fundamental particle which carries one-unit positive charge and mass nearly same as hydrogen atom.”
DISCOVERY OF NEUTRON:
It was discovered by Chadwick. In which he bombarded some light elements with fast moving alpha particles. He found, that some new particles were emitted which carried no charge and had mass equal to that of proton.These neutral particles were named as neutron.
So, neutron is defined as:
“the fundamental particle which carries no charge and mass equal to that of hydrogen atom.”
ATOMIC MODELS OF ATOM
J.J THOMSON PLUM PUDDING MODEL
In 1904, the attempt to explain structure of Atom was done by J.J Thomson.
- Atom is electrically neutral.
- Nucleus is in center.
- In which protons & neutrons are present.
- Outside nucleus electrons revolve like planets revolve around sun.
He said, atom is made of two parts: nucleus and extra nuclear part .
In Nucleus, positive charge is present and in extra nuclear part electrons are present as shown in figure:
Proton -> (+)vely charged
Electron -> (-)vely charged
Neutron -> No charge
Limitation : he failed to explain the stability of an atom”.
According To Electromagnetic theory, a charged particle revolving in circular path continuously emits energy and shorten its path.