1. Chapter 5 Atomic Structure and the Periodic Table
Charles Page High School
Dr. Stephen L. Cotton

2. History of the atom Not the history of atom, but the idea of the atom.
Original idea Ancient Greece (400 B.C.)
Democritus
was a Greek
philosopher.

3. History of Atom Smallest possible piece? Looked at beach Made of sand
Atomos - not to be cut
Looked at beach
Made of sand
Cut sand - smaller sand

4. Another Greek Aristotle - Famous philosopher
All substances are made of 4 elements
Fire - Hot
Air - light
Earth - cool, heavy
Water - wet
Blend these in different
proportions to get all
substances

5. Who Was Right? Greek society was slave based.
Beneath famous to work with hands.
Did not experiment.
Greeks settled disagreements by argument.
Aristotle was more famous.
He won.
His ideas carried through middle ages.
Alchemists change lead to gold.

6. Who’s Next? Late 1700’s - John Dalton- England.
Teacher- summarized results of his experiments and those of others.
Dalton’s Atomic Theory
Combined ideas of elements with that of atoms.

7. Dalton’s Atomic Theory
All matter is made of tiny indivisible particles called atoms.
Atoms of the same element are identical, those of different atoms are different.
Atoms of different elements combine in whole number ratios to form compounds.
Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

8. Just How Small Is an Atom?
Think of cutting a piece of lead into smaller and smaller pieces
How far can it be cut?
An atom is the smallest particle of an element that retains the properties of that element

9. Structure of the Nuclear Atom
OBJECTIVES:
Describe the structure of an atom, including the location of the protons, electrons, and neutrons with respect to the nucleus.

10. Parts of Atoms J. J. Thomson - English physicist. 1897
Made a piece of equipment called a cathode ray tube.
It is a vacuum tube - all the air has been pumped out.

11. Thomson’s Experiment
Voltage source - +
Vacuum tube
Metal Disks

12. Thomson’s Experiment
Voltage source - +

13. Thomson’s Experiment
Voltage source - +

14. Thomson’s Experiment
Voltage source - +

15. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

16. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

17. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

18. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

19. Thomson’s Experiment
Voltage source
By adding an electric field

20. Thomson’s Experiment
Voltage source + -
By adding an electric field

21. Thomson’s Experiment
Voltage source + -
By adding an electric field

22. Thomson’s Experiment
Voltage source + -
By adding an electric field

23. Thomson’s Experiment
Voltage source + -
By adding an electric field

24. Thomson’s Experiment
Voltage source + -
By adding an electric field

25. Thomson’s Experiment
Voltage source + -
By adding an electric field he found that the moving pieces were negative

26. Other particles
Proton - positively charged pieces 1840 times heavier than the electron – by E. Goldstein
Neutron - no charge but the same mass as a proton – by James Chadwick (Jimmy Neutron?)
Where are the pieces?

27. Rutherford’s experiment
Ernest Rutherford -English physicist. (1910)
Believed in the plum pudding model of the atom (discussed in Chapter 13).
Wanted to see how big they are.
Used radioactivity.
Alpha particles - positively charged pieces- helium atoms minus electrons
Shot them at gold foil which can be made a few atoms thick.

28. Rutherford’s experiment
When an alpha particle hits a fluorescent screen, it glows.
Here’s what it looked like

29. Fluorescent
Screen
Lead block
Uranium
Gold Foil

30. He Expected
The alpha particles to pass through without changing direction very much.
Because…?
…the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles.

31. What he expected

32. Because

33. He thought the mass was evenly distributed in the atom

34. Since he thought the mass was evenly distributed in the atom

35. What he got

36. How he explained it Atom is mostly empty.
Small dense, positive piece at center.
Alpha particles are deflected by it if they get close enough. +

37. Most particles pass through, some are deflected by small dense positive area.+

38. Density and the Atom
Since most of the particles went through, it was mostly empty space.
Because the pieces turned so much, the positive pieces were heavy.
Small volume, big mass, big density.
This small dense positive area is the nucleus.

39. Subatomic particles – p.550
Relative
mass
Actual
mass (g)
Name
Symbol
Charge
Electron e- -1
1/1840
9.11 x 10-28
Proton p+ +1 1
1.67 x 10-24
Neutron n0 1
1.67 x 10-24