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J.j. Thomson Atomic Theory
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Introduction to J.J.Thomson atomic theory:Thomson discovered the electron in the year 1897. His work put forward a new
theory, that atom was made up of small particles.Thus he discovered the
electrons. He proved his theory using the cathode ray tube.
Scientists had already done many experiments to find the structure of the atom.
They passed an electric current through a vacuum tube. They saw a light glowing
inside the tube. It travelled in a straight line. They could not explain the
phenomenon. Thomson did more experiments on the cathode tube. He placed
two electric plates on its path. One was positively charged. The other was
negatively charged. The glowing light bent towards the positively charged
plate.and found that the glowing materials bent towards the positively charged
plate. He found out that the glowing light were smaller particles. They were
smaller than the atom. Thus Thomson found the particle called electron. Thus
J.J.Thomson's atomic theory was found.
Thomson suggested that the electrons came out ofthe trace gas that was inside
the cathode tube. Thus a new theory that atoms were made of tiny particles
surfaced.
Thomson discovered the electrons and it was proved that atoms were made up of
protons, electrons and neutrons. Thus
Thomson proved that the atom was divisible. Since the atom was neutral,
Thomson suggested that the negatively charged electron equalled the positively
charged proton and neutrons had no charges.Thomson suggested to consider
the atom as a sphere. It has positively charged particles The positively
chargedparticles is surrounded by the negatively charged electons.The electrons
were placed there due to electrostatic forces.
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J.j.thomson's Experiment for his Atomic Theory
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Thomson used a cathode tube for his experiment.
J.J.Thomson used a highly evacuated discharge tube. He placed two anodes
inside the tube. He fixed twp plates parallel to
each other inside the tube. He passed a thin cathode ray through the pinhole of
the tube. He could see the sides of the tube
glowing in green color. The glow travelled in a straight line. The green glow was
caused by the cathode rays. Now Thomson applied an electric field. The ray
deflected to the positively charged plate. The blue line in the above picture
shows the deflection. Thus Thomson discovered the electrons.
J.j. Thomson Atomic Theory - Properties of Electrons:Back to Top (http://www.tutorvista.com/science/jj-thomson-atomic-theory-0#top)
The properties of electrons were found out by experiments.
1 . When a maltese cross was placed in its path, a shadow of the cross was seen
on the wall of the tube opposite to the cathode.. If the cross was lowered, its
shadow disappeared. Thus it was found out that electrons travelled in a
straight line.
2. When a light wheel of mica was placed in the path of the cathode rays, the
wheel started rotating towards the anode. This
proved that the cathode rays especially the electrons have momentum and
kinetic energy.
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3. A platinum strip was placed at the centre of the concave shaped cathode. The
platinum was blackened. When the
cathode rays struck the platinum, the strip became red hot. This shows that
electrons produce heat when they strike
an object.
4. X-rays are emitted by the electrons.
5.When electric field and magnetic field are applied, the electrons
deflect.
6. Electrons travel with high velocities.
7.Electrons produce fluorescence when they strike crystals, minerals an salts.
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