Olympiad: 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.