discovery of subatomic particles

Electron - Discharge Tube experiments These experiments were conducted in detail by J.J. Thomson and he studied the passage of electricity through gases at extremely low pressure in a cylindrical glass tube. It was discovered that at extremely low pressure, gases become conductors of e..

The whole mass of an atom is due to the nucleus, which means that the nucleus must contain protons equal to the mass of the atom. As the number of protons is equal to the atomic number, the atomic mass should be equal to the atomic number. But for all atoms except hydrogen the atomic mass is found..

Discovery of Radioactivity - The discovery of the phenomenon of radioactivity was purely accidental. In 1896, Henry Becquerel, a French scientist accidentally found that in presence of salt of uranium, photographic plates got heavily fogged even though they were wrapped in opaqu..

Since the atom is electrically neutral there must be positively charged particles present in the atom to neutralize the negative charges of the electrons. Goldstein experimentally proved the existence of protons in the ato..

Search for the missing particle - Although Rutherford's model was enormously successful at explaining the scattering of alpha particles, there was a problem when the experimental data were used to calculate the mass of the nucleus. From the results of the scattering experiments,..

Production of cathode rays - In 1885, Sir William Crookes carried out a series of investigations into the behaviour of metals heated in a vacuum. The experiment of Crookes and others showed that a heated cathode produced a stream of radiation, which could cause gases at low pressure to glow and whi..

Ernest Rutherford, an energetic Scientist From New Zealand working in England, was studying the properties of particles spontaneously emitted by radioactive substances. Of particular interest was a positively charged, relatively heavy emission named alpha particle. Quantities ..

Discovery of Radioactivity and Nature of Radiations - In 1896, the phenomenon of radioactivity was accidentally discovered by French scientist Henri Becquerel. He was performing experiments with uranium compounds. He accidentally placed a crystal of potassium uranyl sulphate over photogra..

/c to photons of energy h u . The elastic scattering of a photon from an electron at rest can be worked out by using the principles of conservation of energy and conservation of momentum. The discovery in 1905 of the dual nature of light was followed by the discovery of dual na..

In view of new discoveries about atoms, Dalton's atomic theory was modified as given below: Atom is no longer indivisible as it has a complex structure of sub atomic particles (electrons, protons and neutrons). Atoms of the same element may posses different relative masses (isot..