Discovery Of Electron, Proton, And Neutron

For a long time, the atom was thought to be the final structure of an element. that changed in 1897, when the English physicist J.J. Thomson discovered electrons as part of subatomic particles, i.e., particles that make up the atom. He did this by performing the famous cathode ray tube experiments. According to Dalton’s atomic theory, atoms are the smallest particles of an element that have the same property as the element and can never be created or destroyed. However, if we break the atom further, we will get electrons, protons, and neutrons. These three particles are the only ones that make up an atom. Each atom of a given element will have identical physical properties because it contains the same subatomic particle as the other one.  Because they have no known components or structure, they are thought to be elementary atom particles. The electron is denoted by the symbol e- and has one negative elementary charge. The first fundamental particle that was discovered by scientists was the electron. J.J. Thomson is credited with discovering the electron and its properties through experiments in a discharge tube. He proposed that electrons are necessary constituents of all atoms. J.J. Thomson conducted experiments in a discharge tube using gas at a low pressure of 0.01mm Hg. This experiment is called the Cathode ray tube experiment.

Definition of Electron

The electron is a negatively charged particle having a low mass. As a result, it is easily deflected when it comes into contact with other electrons or the positive nucleus of an atom.

J.J. Thomson and the discovery of the electron

• J.J. Thomson, a physicist, started an experiment with cathode ray tubes in the late 1800s.

• A Cathode ray tube is a glass tube sealed with a vacuum from which most of the air is taken out.

• A charge was placed across two electrodes at one end of the tube, causing a beam of particles to flow from the cathode (the negatively charged electrode) to the anode (the positively charged electrode) (the positively-charged electrode).

• Because the particle beam or “cathode ray” originates at the cathode, the tubes are known as cathode ray tubes.

• The ray can be detected by applying phosphors to the far end of the tube beyond the anode.

• When the cathode ray strikes the phosphors, they spark or emit light.

• Thomson surrounded the cathode ray with two oppositely charged electric plates to test the properties of the particles.

• The cathode ray was deflected away from the negatively charged electric plate and towards the positively charged plate.

• This implied that the cathode ray was made up of negatively charged particles.

• Further, Thomson put two magnets on either side of the tube which led to the observation that this magnetic field deflected the cathode ray too.

• Thomson discovered the mass-to-charge ratio of the cathode ray particles with the help of these experiments, which led to an interesting discovery— that the mass of each particle was much, much smaller than that of any known atom.

• Thomson repeated his experiments with various metals as electrode materials and discovered that the properties of the cathode ray remained constant regardless of the cathode material.

• This experiment led Thomson to the following conclusions: –

• Cathode rays are made up of negatively charged particles.

• Because the mass of each particle is only 1/2000 of the mass of a hydrogen atom, they must be part of the atom.

• These subatomic particles are present in all elemental atoms.

Properties of Electrons

The properties of Electrons are as stated as below: –

• An electron is one of the fundamental particles with a negative charge.

• It is denoted as e-

• The properties of electrons are independent of the gas in the discharge tube.

• The Electron has a negative mass and its charge is -1

• An electron has an extremely small mass. It has a mass of 1/1840 that of a hydrogen atom (9.108  × 10^-28 g), so its mass is considered almost negligible. (Hydrogen is the atom that has the lowest mass.) Because the mass of a hydrogen atom is 1 u, the relative mass of an electron is 1/1840 u.

• An electron has an absolute mass of 9.1 × 10^-28 grams.

• It has a charge of one unit negative charge, or 1.602 × 10^-19 coulombs.

• The tiny electrons move in specific orbits or shells around the nucleus of the atom.

Conclusion

Sir J. J. Thomson was the first to demonstrate the existence of electrons, which are negatively charged particles that exist within an atom. Thus, the electron was the first sub-atomic particle discovered, laying the foundation for the discovery of all other sub-atomic particles (protons and neutrons) as well as the atomic structure itself.