Discovery Of Proton, Neutron, Properties, Important Points, JEE Chemistry 2024

Discovery of Proton : Protons are subatomic particles carrying a positive charge, quantified as +1.602 × 10 ^–19 Coulombs , and possess a mass of 1.672 × 10 ^–27 kg . With the exception of hydrogen nuclei, all atomic nuclei consist of protons and neutrons, the latter being electrically neutral particles comprising a single proton.

Each element's nucleus contains a consistent number of protons, determining its atomic number and placement within the periodic table. When the count of protons in the nucleus matches the number of electrons orbiting it, the atom attains electrical neutrality.

Neutrons are subatomic particles with no charge. Due to differences in the number of neutrons in their respective nuclei, the masses of two distinct isotopes of an element differ.

Discovery of Proton

Discovery of Proton : Since the atom as a whole is electrically neutral and the presence of negatively charged particles in it was established, therefore it was thought that some positively charged particles must also be present in the atom. So, during the experiments with cathode rays, the scientist Goldstein designed a special type of discharge tube. He discovered new rays called Canal rays . The name canal rays is derived from the fact that the rays travelled in straight line through a vacuum tube in the opposite direction to cathode rays, pass through and emerge from a canal or hole in the cathode. They are also known as anode rays.

• They travel in straight lines.
• The value of the charge on the particles constituting the anode rays is found to depend on the nature of gas taken.
• The mass of the particles constituting the anode rays is found to depend on the nature of gas taken.
• The charge to mass ratio(e/m) of the particles is also found to depend on the gas taken.
• Their behaviour in electric and magnetic field is opposite to that observed for electron.

These rays are believed to be produced as a result of the knock out of the electrons from the gaseous atoms by the bombardment of high-speed electrons of the cathode rays on them. These anode rays are not emitted from the anode but are produced in the space between the anode and the cathode. The lightest positively charged particles were obtained when the gas taken in the discharge tube was hydrogen. The e/m value. of these particles were maximum. They had minimum mass and unit positive charge. The particle was called a proton.

Charge on a Proton  = +1.6022 × 10 ^–19 C

Mass of a Proton = 1.672 × 10 ^–27 kg

Discovery of Neutron

Discovery of Neutron : In 1920, Rutherford suggested that in an atom, there must be present at least a third type of fundamental particles which should be electrically neutral and posses mass nearly equal to that of proton. He proposed the name for such fundamental particles as neutron. In 1932, Chadwick bombarded beryllium with a stream of α-particles. He observed that penetrating radiations were produced which were not affected by electric & magnetic fields. These radiations consisted of neutral particles, which were called neutrons. The nuclear reaction can be shown as

Thus, a neutron is a sub atomic particle which has a mass 1.675×10 ^–27 kg (same as proton) approximately 1amu, or nearly equal to the mass of proton or hydrogen atom and carrying no electrical charge.

• The e/m value of a neutron is zero.

Important Points To Remember

• Atom is actually made of 3 fundamental particles:

1. Electron

2. Proton

3. Neutron

Order of Specific Charge