Andhra Pradesh PSC: 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.


  • The electron is a fundamental particle of an atom which carries a unit negative charge.

  • It was discovered by J.J. Thomson in 1897.


  • It is a fundamental particle of an atom carrying a unit: positive charge.

  • It was discovered by Rutherford and Goldstein in 1886.


  • 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.

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