1. What does an atom look like?
How did scientists figure out what it looks like?

2. Atomic Theory

3. Democritus Smallest piece of all matter is not divisible
He named the smallest piece of matter “atomos,” meaning “not to be cut.”

5. John Dalton 1760-1844 Father of Modern Atomic Theory
matter is made of atoms
atoms in an element are identical
different elements have different atoms
atoms maintain their mass even in a chemical reaction

6. J.J. Thomson
1897

7. When a magnet was placed near the beam of light, it separated into two parts

8. When a magnet was placed near the beam of light, it separated into two parts

9. Thomson Model
Where did they come from?
This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from?

10. Thomson Model
Proposed a model of the atom that is sometimes called the “Plum Pudding” model.
a sphere
with negatively charged electrons scattered.

11. J.J. Thomson
1897
discovered electrons (charged particles)

13. Rutherford
Using atoms to see what is inside
of other atoms

14. Rutherford

15. Rutherford Experiment Molecular Expressions

16. Rutherford’s experiment: Discovery of the Nucleus
Most of positively charged particles Rutherford shot at the gold foil passed right through without changing course at all.
However, some did bounce away from the gold sheet as if they had hit something solid.
He knew that positive charges repel positive charges.
Rutherford found the Nucleus

17. Rutherford’s model
A nucleus in the center, with electrons moving around in the open space

18. 1) Most of the volume of the atom is ...
empty space

19. 2) Virtually all mass atom found in ...
... the nucleus

20. 3) Strong, positive charge in the center of atom
                              
3) Strong, positive charge in the center of atom

21. Relative Sizes in the Atom Hear Thomson talk the Electron

22. Did you know ... If the atom were the size of a football stadium, the nucleus would be the size of a....  

23.   .... a marble!!! 

25. Bohr Model
Electrons move in definite orbits around the positive nucleus
Like the planets orbiting the sun.
These orbits, or energy levels, are located at certain distances from the nucleus.