, CHEMISTRY STRUCTURE OF THE ATOM
Structure of the Atom
Charged Particles in Matter
The phenomenon of static electricity and conduction of electricity through some substances hints at the
presence of charged particles in matter.
Discovery of the Electron
J.J. Thomson performed an experiment by passing electricity at a high voltage through a discharge
tube containing a gas at a very low pressure. A green fluorescence was seen emitting out from the
other end of the discharge tube.
This fluorescence is the result of rays emitted from the cathode (negative plate) towards the anode
(positive plate) in the discharge tube. Hence, these rays are called cathode rays.
From his experiment, Thomson arrived at the conclusion that cathode rays are nothing but a stream of
negatively charged particles. These negatively charged particles are called electrons.
Discovery of the Proton
A German scientist, E. Goldstein in 1886, modified the discharge tube and passed electric current
through it.
He found that the positively charged rays were emitted from the anode in the discharge tube. These
rays were called canal rays.
When an electric field was applied, these rays deflected towards the negatively charged plate. Thus,
Goldstein concluded that an atom contains positively charged particles along with electrons.
These positively charged particles were named as protons by a British scientist, Ernest Rutherford.
Canal rays were also called anode rays since they were emitted from the anode (electrode connected
to the positive terminal of high voltage source) in the gas discharge experiments using a perforated
cathode.
Discovery of the Neutron
In 1932, James Chadwick observed that when beryllium was exposed to α-particles, different kinds of
particles were emitted.
These particles had about the same mass as protons and carried no electrical charge. Hence,
Chadwick named these particles neutrons.
These were present in the nucleus along with protons.
Neutrons are present in the nucleus of all the atoms except hydrogen.
As protons and neutrons are both present in the nucleus, they are together known as nucleons.
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Structure of the Atom
Charged Particles in Matter
The phenomenon of static electricity and conduction of electricity through some substances hints at the
presence of charged particles in matter.
Discovery of the Electron
J.J. Thomson performed an experiment by passing electricity at a high voltage through a discharge
tube containing a gas at a very low pressure. A green fluorescence was seen emitting out from the
other end of the discharge tube.
This fluorescence is the result of rays emitted from the cathode (negative plate) towards the anode
(positive plate) in the discharge tube. Hence, these rays are called cathode rays.
From his experiment, Thomson arrived at the conclusion that cathode rays are nothing but a stream of
negatively charged particles. These negatively charged particles are called electrons.
Discovery of the Proton
A German scientist, E. Goldstein in 1886, modified the discharge tube and passed electric current
through it.
He found that the positively charged rays were emitted from the anode in the discharge tube. These
rays were called canal rays.
When an electric field was applied, these rays deflected towards the negatively charged plate. Thus,
Goldstein concluded that an atom contains positively charged particles along with electrons.
These positively charged particles were named as protons by a British scientist, Ernest Rutherford.
Canal rays were also called anode rays since they were emitted from the anode (electrode connected
to the positive terminal of high voltage source) in the gas discharge experiments using a perforated
cathode.
Discovery of the Neutron
In 1932, James Chadwick observed that when beryllium was exposed to α-particles, different kinds of
particles were emitted.
These particles had about the same mass as protons and carried no electrical charge. Hence,
Chadwick named these particles neutrons.
These were present in the nucleus along with protons.
Neutrons are present in the nucleus of all the atoms except hydrogen.
As protons and neutrons are both present in the nucleus, they are together known as nucleons.
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