Date post: | 20-Jul-2015 |
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Molecules ?Atom Substances Small
particles
Is atom divisible?Dalton’s theory says ‘No’.
JOHN DALTON (1776 – 1884)
Dalton’s Atomic Theory All matter is made up of small particles called atoms.
Atom is the smallest particle which can engage in a chemical reaction.
All the atoms of an element have the same properties. That is they have the same mass, size and character.
Atoms of different element have different characteristics.
Atoms can neither be created nor destroyed.
Atoms are indivisible.
J J Thompson
DISCOVERY OF ELECTRONES BY J.J. THOMPSON
Discharge tube experiment
Thompson noticed that when electricity was passed through the gas in the discharge tube at a low pressure, the glass walls of the tube at the side of the positive plate were glowing. He found out that some particles formed inside the tube caused this glow.
The inferences arrived by Sir. J.J. Thompson
The cause of the glow is the invisible rays emitted from the negative metal plate of the discharge tube.
It is a flow of particles with negative charge.
There are particles carrying negative charge in all substances.
These particles which had negligible mass were given the name “electron”. The mass of an electron is 1/1837 of the mass of the smallest atom – hydrogen.
Ruther ford
DISCOVERY OF PROTONS BY RUTHER FORD
Ruther ford discovered protons. They have positive charge and mass equal to
that of a hydrogen atom.
GOLD FOIL EXPERIMENT
Findings of Ruther ford Atom has a central part .He called it as nucleus.
Nucleus has positive charge
Compared with the total volume of an atom the volume of the nucleus is very meager.
The mass of an atom is concentrated in the nucleus.
Electrons are distributed in the space around the nucleus.
orbit
electrons
Nucleus
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RUTHER FORD’S ATOM MODEL
SOLAR SYSTEM
Universe Atom
Center : Sun
Planets: Revolves around the sun
Orbit: Path through which planets move
Center : Nucleus
Electron: Revolve around the Nucleus
Orbit: Path through which Electrons move
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