structure of atom

3. Small
particles
Substances Molecules Atom ?

4. Is atom divisible?
Dalton’s theory says ‘No’.
JOHN DALTON (1776 – 1884)

5. 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.

6. DISCOVERY OF ELECTRONES BY J.J. THOMPSON
J J Thompson

7. Discharge tube experiment

8. 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.

9. DISCOVERY OF PROTONS BY RUTHER FORD
Ruther ford

10. Ruther ford discovered protons. They
have positive charge and mass equal to
that of a hydrogen atom.

11. GOLD FOIL EXPERIMENT

12. 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.

13. orbit
RUTHER FORD’S ATOM MODEL
electrons
Nucleus
1

14. SOLAR SYSTEM

15. 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

16. THANK YOU