STRUCTURE
OF
ATOM

e-Book prepared by

Rugma Nair
B.Ed. Physical Science
Peet Memorial Training College
Mavelikkara

Atoms are basic unit of matter and defining structure of elements

John Dalton(1766-1844)

John Dalton proposed the Atomic Theory in 1807 for the study of atoms and for finding how matter has been formed.

According to Dalton, matter is made up of indivisible atoms

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SIR HUMPHREY DAVY(1778-1829)

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Sir Humphrey Davy used electricity to isolate many elements like Na, K, Ca, Mg etc from their compounds.
Through his experiments he inferred that electric charges are present in substances

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MICHAEL FARADAY(1791-1867)

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Michael Faraday is known as the father of electricity. He found that electricity can pass through liquids. it is found that some liquid substances can be separated into their components by passing electricity through them. But, he failed to explain the reason behind this process

J J THOMSON(1856-1940)

J J Thomson modified the discharge tube experiments by scientists before him. He conducted cathode ray tube experiment and observed the cathode rays. He analysed them under different conditions and proved that the rays contained negatively charged particles with mass and energy, and these particles are identical irrespective of the gas filled in tube. So the particles are part of atom and known as Electrons. Thus, he established that atom is divisible

CATHODE RAY TUBE EXPERIMENT

ERNEST RUTHERFORD(1871-1937)

Even though Eugen Goldstein recognized the presence of positive charge in atoms in 1886, it was Rutherford who proved it authentically. Through his alpha ray scattering experiment, he substantiated that major portion of atom is empty and there is a small part inside the atom where all positive charge is concentrated. This central region is called Nucleus of the atom. The particles inside the nucleus which are positively charged are called Protons whose charge is equal and opposite to that of electrons.

ALPHA RAY SCATTERING EXPERIMENT

JAMES CHADWICK(1891-1974)

In 1932, Chadwick proved scientifically that inside the nucleus of an atom, there are neutral particles having mass equal to that of protons. This charge-less particle is the Neutron. The total mass of an atom is concentrated in the nucleus because the particles protons and neutrons that posses mass are in the nucleus.