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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