1. From Democritus to Today’s Modern Theory
The History of the Atom
From Democritus to Today’s Modern Theory

3. Democritus 400 BC Proposed that all matter is made up of atoms.
Thought atoms were small, hard particles of different shapes and sizes.
Coined the term ‘Atom’
From the Greek word meaning
‘Can not be divided.’

4. An Apothecary in his Laboratory

5. Alchemists First ‘Chemists’ around 900 AD
First to include observation and experimentation with pure thought methods of science.

6. Antoine Lavoisier

7. Lavoisier 1785 Authored the Law of Conservation of Mass
Did experiments to prove that matter does not disappear during a chemical reaction.
‘Matter can not be created or destroyed, it can only be rearranged.’

8. John Dalton

9. Dalton Father of Modern Atomic Theory 1800’s
All matter consists of atoms with space in between.
Atoms of the same kind of element are identical to each other.
There are as many different kinds of atoms as there are different elements.
Atoms are solid spheres.
‘Billiard Ball Model’

10. Billiard Ball Model

11. J J Thomson

12. Thomson
1904
Inferred that atoms contain small negatively charged particles.
He called them ‘electrons.’
He thought the electrons were dispersed throughout a positively charged sphere.
‘Chocolate Chip Cookie Dough Model’

13. Cookie Dough Model

14. Ernest Rutherford

15. Rutherford 1911 Famous Gold Foil Experiment
Discovered and named the ‘nucleus’ of the atom.
Proposed that most of the mass and all of the positive charges of an atom are in its nucleus.
‘Peach Pit Model’

16. Rutherford’s Gold Foil Experiment

17. Peach Pit Model

18. Niels Bohr

19. Bohr
1913
Concluded that electrons travel in fixed orbits around the nucleus based on the amount of energy they contain.
He called the ‘orbits’ Energy Levels.
‘Solar System Model’

20. Bohr Model

21. Erwin Schrodinger and Werner Heisenberg

22. Schrodinger and Heisenburg
1926
Scientists described the electron region of the atom as a cloud around the nucleus.
This cloud area shows that electrons do not orbit the nucleus in definite paths, but are likely to be in a given region at any particular time.
‘Modern Electron Cloud Model’

23. Modern Electron Cloud Model

24. James Chadwick

25. Chadwick
1932
Worked with E. Rutherford in the discovery of a third sub-atomic particle.
He concluded this particle to be free of electrical charge and he called it the ‘neutron.’
Concluded it was located in the nucleus along with the protons.

26. Chadwick’s Discovery of the Neutron

27. Today’s Newest Members:

28. Quarks and Leptons Particles within particles.
Protons and Neutrons are made of Quarks:
Up Down
Strange Top
Charm Bottom
Electrons are a small thin type of Lepton.

29. And now you know the rest of the story!!
The End.