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J.j. Thomson Atomic Theory — www.tutorvista.com — Readability http://www.readability.com/articles/y1sdmrct tutorvista.com J.j. Thomson Atomic Theory original (http://www.tutorvista.com/science/jj-thomson-atomic-theory-0) 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. 1 of 3 10/7/13 6:52 PM J.j. Thomson Atomic Theory — www.tutorvista.com — Readability http://www.readability.com/articles/y1sdmrct J.j.thomson's Experiment for his Atomic Theory Back to Top (http://www.tutorvista.com/science/jj-thomson-atomic-theory-0#top) 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. 2 of 3 10/7/13 6:52 PM J.j. Thomson Atomic Theory — www.tutorvista.com — Readability http://www.readability.com/articles/y1sdmrct 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. Original URL: http://www.tutorvista.com/science/jj-thomson-atomic-theory-0 3 of 3 10/7/13 6:52 PM