Name the discoverer of electron, proton, and neutron.
Answers
Answer:
Electron-JJ Thomson
Proton - Ernest Rutherford
Neutron - Chadwick
Discovery of Electron
During the latter half of the nineteenth century, it was found that while normally dry gases do not conduct an electric current, they do so under very low pressure and then patches of light are seen. The passage of electricity through gases as studied by a number of physicists, particularly by Faraday, Davy, Crookes and J.J. Thomson.
When a current of high voltage (10,000 volts) is passed through a gas of air kept at a very low pressure (0.01 – 0.03 mm) blue rays are seen emerging from the case. These rays are called “Cathode Rays”.
Cathode ray discharge tube
Some of the important properties of the cathode rays studied by Sir J.J. Thomson and others are given below:
Cathode rays come out at right angles to the surface of the cathode and move in straight lines.
Their path is independent on the position of the anode.
They produce phosphorescence on certain salts like ZnS and fluorescence on glass.
They blacken photographic plates.
The rays pass through thin sheet of metals. If the metal sheet is too thick to be penetrated the rays cast a shadow.
They produce X-ray when they strike a metal.
The rays ionize a gas through which they pass.
They heat a substance on which they fall.
Discovery of Proton
Positive rays or Canal rays
Atoms are electrically neutral. Hence after the discovery of the negatively charged constituent (electron) of an atom, attempts were made to discover the positively charged counterpart of electrons. By using a discharge tube containing a perforated cathode. Goldstein (1886) found that some rays passed through these holes in a direction opposite to that of the cathode rays.These are also known as anode rays because they seems to be coming from a perforated anode used in a discharge tube experiment. These are made up of positively charged particles known as protons.
The charge to the mass ratio (e/m ratio ) is not constant for these rays, and has been found different for different gases used in the discharge tube.
These are called the positive rays or canal rays. J.J. Thomson (1910) measured their charge by mass ratio from which he was able to deduce that these contain positive ions. Their properties are:
They are positively charged.
The positive charge is either equal to or whole number multiple of the charge on an electron.When hydrogen gas was filled in the discharge tube the positive charge on the positive rays was equal to the negative charge on an electron, and the mass was less than the hydrogen atom.
The deflection of positive rays under the influence of an electric or magnetic field is smaller thanthat of the cathode rays for the same strength of field. This shows that the positive rays have a greater mass than that of electrons.
The mass of the positive rays depends on the atomic weights or molecular weights of the gases in the discharge tube. The charge/mass ratio also varies because the change in positive charge on the rays. It may be either equal to or integral multiple of the charge on an electron.
The lightest of all particles identified in positive rays from different elements was one with a mass very slightly less than that of hydrogen atom (or nearly equal to H-atom). The lightest positively charged particle is called a proton (P or P+). Positive rays are atomic or molecular resides from which some electrons have been removed. The removed electrons constitute the cathode rays and the positive residues form the positive or canal rays.
Discovery of Neutron
After the discovery of electron and proton Rutherford (1920) had predicted the existence of a neutral fundamental particle. In 1932, Chadwick bombarded the element Beryllium with a-particles and noticed the emission of a radiation having the following characteristics.
The radiation was highly penetrating
The radiation was unaffected by magnetic and electric fields which show that it is electrically neutral.
It was found to have approximately the same mass as the protons.
The name ‘neutron’ was given to this sub-atomic particle. It is denoted by n or 1on. Bombardment of beryllium by α-particles results in the formation of carbon and neutrons are emitted.
At present there are a number of evidences which confirm that like electron, proton and neutron is also a fundamental constituent of atoms (a single exception is 11H atom which does not contain any neutron)
Mass of a neutron is 1.008930 amu (1.6753 x 10–24g or 1.6753 x 10–27 kg)
Neutron “A sub-atomic particle, which is a fundamental constituent of matter having mass approximately equal to the hydrogen atom and which is electrically neutral, is called a