Discovery of Electron

Discovery of Electron

In 1830, Michael Faraday showed that if electricity is passed through a solution of an electrolyte, chemical reactions occurred at the electrodes, which resulted in the liberation and deposition of matter at the electrodes. He formulated certain laws. These results suggested the particulate nature of electricity.

An insight into the structure of atoms was obtained from the experiments on electrical discharge through gases. Before we discuss these results we need to keep in mind a basic rule regarding the behavior of charged particles : “Like charges repel each other and unlike charges attract each other”.

In mid 1850s many scientists mainly Faraday began to study electrical discharge in partially evacuated tubes, known as Cathode ray discharge tubes.

                                      

A cathode ray tube is made of glass containing two thin pieces of metal, called electrodes, sealed in it. The electrical discharge through the gases could be observed only at very low pressures and at very high voltages. The pressure of different gases could be adjusted by evacuation. When sufficiently high voltage is applied across the electrodes, current starts flowing through a stream of particles moving in the tube from the negative electrode (cathode) to the positive electrode (anode). These were called cathode rays or cathode ray particles. The flow of current from cathode to anode was further checked by making a hole in the anode and coating the tube behind anode with phosphorescent material zinc sulphide. When these rays, after passing through anode, strike the zinc sulphide coating, a bright spot on the coating is developed.

The results of these experiments are summarized below :-

• The cathode rays starts from cathode and move towards the anode.
• These rays themselves are not visible but their behavior can be observed with the help of certain kind of materials (fluorescent or phosphorescent) which glow when hit by them. Television picture tubes are cathode ray tubes and television pictures result due to fluorescence on the television screen coated with certain fluorescent or phosphorescent materials.
• In the absence of electrical or magnetic field, these rays travel in straight lines.
• In the presence of electrical or magnetic field, the behaviors of cathode rays are similar to that expected from negatively charged particles, suggesting that the cathode rays consist of negatively charged particles,  suggesting that the cathode rays consist of negatively charged particles, called electrons.
• The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.

Thus, we can conclude that electrons are basis constituent of all the atoms.