NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Atomic Structure
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Atomic Structure
- In 1809, Dalton suggested that atom is the smallest particle of the element and it is indivisible.
- But in the beginning of 20th century Rutherford, J. J. Thomson and more suggested that atom is divisible and made up of electrically charged particles.
Electron
- The electron is a fundamental particle of an atom which carries a unit negative charge.
- It was discovered by J. J. Thomson in 1897.
Proton
- It is a fundamental particle of an atom carrying a unit: positive charge.
- It was discovered by Rutherford and Goldstein in 1886.
Neutron
- It is a fundamental particle of an atom carrying no charge.
- It was discovered by Chadwick in 1932.
Properties of Cathode Rays
- They travel in straight: lines.
- They cast shadow of solid objects placed in their path.
- They cause mechanical motion, i.e.. , they consists of material particles.
- They carry negative charge.
- These rays are deflected when magnetic field is applied on them.
- They produce heating effect.
- They cause ionization of gas through which they pass.
- They affect the photographic plates.
- They have penetrating power.
Properties of Anode Rays
- They travel in straight lines, however, their speed in much less than that of cathode rays.
- They are made up of material particles.
- They are positively charged.
- They deflect in electric and magnetic field.
Properties of Nucleus
- Nucleus of an atom consists of protons and neutrons, which are collectively known as nucleons.
- Density of nucleus is enormous and is of order of 1014 g/cm.
- Instability of the nucleus is due to high neutron proton ratio.