1. UP AND ATOM
It’s time for…
THE HISTORY OF THE ATOM !

2. Democritus (400 B.C.)
First person to propose that matter is made of about 100 tiny particles called atoms that collide and combine to make everything.
His theory was not widely believed, even though it turned out to be correct.
Like other scientists of his time, he had no real evidence for his ideas.

3. Aristotle -- 350 B.C. FIRE WATER EARTH AIR
Denied the existence of atoms.
Said matter consisted of combinations of only four elements -- air, earth, fire, and water.
Was widely respected, and his ideas formed the basis of science for nearly 2000 years.
Lead to alchemy and superstition.
FIRE
AIR
EARTH
WATER

4. The Dark Ages of Chemistry
400 B.C A.D.
The Dark Ages of Chemistry
The idea of atoms
was lost

5. Robert Boyle 1661 Renews belief in the idea of atoms through his
experiments
with gases

6. Conservation of Matter
Antoine Lavosier 1780
Modern
Chemistry
Father of
Modern Chemistry
Antoine
Developed the theory of
Conservation of Matter

7. John Dalton --1800 (a.k.a “the marble guy”)
Atoms are all solid with uniform density
Atoms are the smallest particles of nature
All atoms of the same element are identical
Atoms of different sizes can combine to form compounds
An atom
(Close-up view)

8. Discovers a negatively charged beam in an electrified vacuum tube.
1879 William Crookes
Discovers a negatively charged beam in an electrified vacuum tube.

9. Proved that Crookes’ negative “beam” was really particles he called “electrons”.
Realized that these electrons must be smaller than the atom
Developed the “Plum Pudding” model of the atom
First person to realize that atoms are made of small parts
J.J. Thomson
1897

11. What is plum pudding? I prefer mint chocolate Chip ice cream
Atoms are negative electrons stuck in a positive glob

12. Ernest Rutherford - 1911 Performed Gold Foil Experiment
Won Nobel Prize for Chemistry

13. The Gold Foil Experiment
Bombard thin piece of gold foil with alpha particles
Result: a few are deflected while most are unaffected
What does it all mean?

14. What Happened?

15. What Does it Mean? Atoms have dense area in the middle
The nucleus
The proton
Electrons travel around away from the nucleus
The atom is mostly empty space

16. NIELS BOHR 1913 Was a friend of Einstein
Developed important ideas of quantum physics and atomic structure
Use light spectrum to explain the structure of the atom

17. Light Spectrum

18. Niels Bohr
Compares electrons orbiting the nucleus of an atom to planets orbiting around the sun.
Electrons occupy distinct orbitals.
Orbitals have certain energies and distances from the nucleus.

19. Erwin Schrodinger
Regions where electrons are most likely found are called “electron clouds”.
Different types of orbitals have different shapes and different levels of energy.
Although difficult to understand, the results were spectacular!
This new model of the atom explained the physical properties of atoms, and the Periodic Table, perfectly.

20. Discovered the neutron
James Chadwick 1932
Discovered the neutron
neutron
Predicted by Rutherford in1920, but very difficult to detect.
New tool for probing and changing the nucleus of an atom.

21. 1980’s
The first atoms are seen with scanning tunneling microscopes

22. 1995 Fermi lab scientists in Batavia,
Illinois study and detect six types
Of quarks
Quarks are particles believed to
Make up protons and neutrons