Q) write in brief-
a) discovery of an atom
b) discovery of an electron
c) discovery of an proton
d) discovery of an neutron
Q) write in brief-
a) discovery of an atom
b) discovery of an electron
c) discovery of an proton
d) discovery of an neutron
a) Discovery of an atom:
At first, atom was termed by Democritus, around 400 B.C when he termed that smallest particle of matter as atom.The experimental chemistry took its place in 18th centuray after the discovery of oxygen and hydrogen. Then a scientist name A. L. Lavoisier , gave the concept of elements and on this basis Laws of chemical Combinations was derived. Then came a scientist John Dalton , gave the atomic theory and suggested the idea of the atom as being the smallest particle of all the matter. And existence of atom was proved by discovery of electron, proton and neutron only.
b) Discovery of electron :
Thomson's Experiment (Discovery of electron)
According to the theory, a discharge tube (which is a long glass tube) is taken about 60cm long and sealed that tube at both the ends and fitted with two metal electrodes. It has a side tube fitted with a stop - cock.
Now , this tube is connected to a vacuum pump and the pressure inside the tube is lowered by using this pimp and maintained to 0.01 mm.A high voltage electricity of about 10,000 V is applied between the electrodes and the result is abtained.
Observation:
1.Some invisible rays are emitted from the -ve cathode which makes a greenish glow at the opposite wall of discharge tube.
2. The rays coming from cathode , produces a shadow if a solid object is placed between the two electrodes; which explains that cathode rays travel in a straight line.
3. If an external electric field is applied, the cathode rays are deflected towards the +ve anode , so the rays must carry a negative charge.
4. They strike the metal foils and causes heating effect .
5.They cause ionization of the gas in the discharge tube and produce X-rays when fall over hard metals like Tungstun, Molybdenum etc.
6.They affect the photographic plates.
Conclusion:
1.The cathode rays are made up of material particles.
2.They carry -ve charge.
Hence, the above experiment explains that, cathode rays are negatively charged material particles called as ELECTRONS.
c) Discovery of proton :
Goldstein Experiment(Discovery of proton)
The proton was discovered during the study of canal ray in gas discharge tube experiment. Goldstein discovered positive rays through a gas discharge tube experiment.
The perforated cathode was used in this discharge tube. When a high voltage of about 10,000 volts is applied to a discharge tube having a perforated cathode and containing air at very low pressure of about .001 mm of mercury, a faint red glow was observed behind the cathode. The rays were generated from anode so they are known as anode rays or canal rays or positive rays.J.J. Thomson and Wilhelm When studied further about positive rays and concluded that canal rays are made of positively charged particles so moving towards cathode which is a negatively charged electrode. The magnitude of charge by mass ratio depends on the nature of gas present in discharged tube.The mass of lightest particle of canal rays was observed. It is found equals to the mass of one hydrogen atom. This positively charged particle is called as proton.
d) Discovery of neutron :
In 1932, James Chadwick bombarded beryllium (Be) with alpha a prticles. He allowed the radiation emitted by beryllium to incident on a paraffin wax. It was found that protons were shot out form the paraffin wax. People began to look for what was in the "beryllium radiation".Some people suggested that the radiation may be gamma radiation. However, Chadwick found that the radiation could not be gamma radiation since energy and momentum were not conserved in its production. He showed that all the observations could be explained if the radiation consisted of neutral particles of mass approximately equal to that of proton. This neutral particle was named neutron.
At first, atom was termed by Democritus, around 400 B.C when he termed that smallest particle of matter as atom.The experimental chemistry took its place in 18th centuray after the discovery of oxygen and hydrogen. Then a scientist name A. L. Lavoisier , gave the concept of elements and on this basis Laws of chemical Combinations was derived. Then came a scientist John Dalton , gave the atomic theory and suggested the idea of the atom as being the smallest particle of all the matter. And existence of atom was proved by discovery of electron, proton and neutron only.
b) Discovery of electron :
Thomson's Experiment (Discovery of electron)
According to the theory, a discharge tube (which is a long glass tube) is taken about 60cm long and sealed that tube at both the ends and fitted with two metal electrodes. It has a side tube fitted with a stop - cock.
Now , this tube is connected to a vacuum pump and the pressure inside the tube is lowered by using this pimp and maintained to 0.01 mm.A high voltage electricity of about 10,000 V is applied between the electrodes and the result is abtained.
Observation:
1.Some invisible rays are emitted from the -ve cathode which makes a greenish glow at the opposite wall of discharge tube.
2. The rays coming from cathode , produces a shadow if a solid object is placed between the two electrodes; which explains that cathode rays travel in a straight line.
3. If an external electric field is applied, the cathode rays are deflected towards the +ve anode , so the rays must carry a negative charge.
4. They strike the metal foils and causes heating effect .
5.They cause ionization of the gas in the discharge tube and produce X-rays when fall over hard metals like Tungstun, Molybdenum etc.
6.They affect the photographic plates.
Conclusion:
1.The cathode rays are made up of material particles.
2.They carry -ve charge.
Hence, the above experiment explains that, cathode rays are negatively charged material particles called as ELECTRONS.
c) Discovery of proton :
Goldstein Experiment(Discovery of proton)
The proton was discovered during the study of canal ray in gas discharge tube experiment. Goldstein discovered positive rays through a gas discharge tube experiment.
The perforated cathode was used in this discharge tube. When a high voltage of about 10,000 volts is applied to a discharge tube having a perforated cathode and containing air at very low pressure of about .001 mm of mercury, a faint red glow was observed behind the cathode. The rays were generated from anode so they are known as anode rays or canal rays or positive rays.J.J. Thomson and Wilhelm When studied further about positive rays and concluded that canal rays are made of positively charged particles so moving towards cathode which is a negatively charged electrode. The magnitude of charge by mass ratio depends on the nature of gas present in discharged tube.The mass of lightest particle of canal rays was observed. It is found equals to the mass of one hydrogen atom. This positively charged particle is called as proton.
d) Discovery of neutron :
In 1932, James Chadwick bombarded beryllium (Be) with alpha a prticles. He allowed the radiation emitted by beryllium to incident on a paraffin wax. It was found that protons were shot out form the paraffin wax. People began to look for what was in the "beryllium radiation".Some people suggested that the radiation may be gamma radiation. However, Chadwick found that the radiation could not be gamma radiation since energy and momentum were not conserved in its production. He showed that all the observations could be explained if the radiation consisted of neutral particles of mass approximately equal to that of proton. This neutral particle was named neutron.
