Atom is the smallest indivisible particle of the matter. Atom is made of electron, proton and neutrons.
PARTICLE |
ELECTRON |
PROTON |
NEUTRON |
Discovery |
Sir. J. J. Thomson |
Goldstein( 1886) |
Chadwick( 1932) |
|
( 1869) |
|
|
Nature of charge |
Negative |
Positive |
Neutral |
Amount of charge 1.6 x 10-19 Coloumb 1.6 x 10-19 Coloumb 0 |
Mass |
9.11 x 10-31 kg |
1.672614 x 10-27 kg 1.67492 x10-27 kg |
Electrons were discovered using cathode ray discharge tube experiment.
Nucleus was discovered by Rutherford in 1911.
Cathode ray discharge tube experiment: A cathode ray discharge tube madeof glass is taken with two electrodes. At very low pressure and high voltage, current starts flowing through a stream of particles moving in the tube fromcathode to anode. These rays were called cathode rays. When a perforatedanode was taken, the cathode rays struck the other end of the glass tube atthe fluorescent coating and a bright spot on the coating was developed
Results: a. Cathode rays consist of negatively charged electrons. b. Cathode rays themselves are not visible but their behavior can be observed with help of fluorescent or phosphorescent materials. c. In absence of electrical or magnetic field cathode rays travel in straight lines d. In presence of electrical or magnetic field, behaviour of cathode rays is similar to that shown by electrons e. The characteristics of the cathode rays do not depend upon the material of the electrodes and the nature of the gas present in the cathode ray tube.