1. Atomic Structure and Periodicity
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

2. Dalton’s Atomic Theory (1808)
Each element is made up of tiny particles called atoms.
The atoms of a given element are identical; the atoms of the same elements have the same chemical and physical properties
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

3. Dalton’s Atomic Theory (continued)
Atoms of different elements are different. the atoms of different elements are different in some fundamental way or ways.
Chemical reactions involve reorganization of the atoms - changes in the way they are bound together. Atoms can combine in whole number ratios to form compounds
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

4. Early Experiments to Characterize the Atom
J. J. Thomson - postulated the existence of electrons using cathode ray tubes.
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

5. Deflection of Cathode Rays by an Applied Electric Field
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

6. Diagram of the Millikan Apparatus
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
R. A. Millikan (1909)
Determined the charge on the electron.
How could he calculate the mass?
e = 1.60 x C
e/m = 1.76 x 108 C/g
m = 9.09 x g
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

8. The Plum Pudding Model of the Atom
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Ernest Rutherford - explained the nuclear atom, containing a dense nucleus with electrons traveling around the nucleus at a large distance.
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

10. Rutherford: a student of JJ Thomson started with plumb pudding
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

11. Rutherford’s Experiment on a-particle Bombardment of Metal Foil
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

12. Expected and Actual Results of Rutherford’s Experiment
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
What happened
Most alpha particles passed straight through undeflected.
Surprisingly, a significant number deflected through moderate angles
Some scattered back from where they had come.
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Famous Quote
“It was quite the most incredible event that has ever happened to me in my life. It was almost as if you fired a 15 inch shell into a piece of tissue paper and it came back and hit you”
-Earnest Rutherford
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

15. Significance of the Gold Foil Experiment
The fact that most of the alpha particles went straight through undeflected indicated that the atom is mostly space.
The ease with which electrons could be removed led Rutherford to believe that electrons occupied this space.
Copyright©2000 by Houghton Mifflin Company. All rights reserved.

16. Significance of the Gold Foil Experiment
The fact that some of the alpha particles were deflected suggested that the positive charge (and most of the mass) in the atom was concentrated in a very dense nuclear center.
It was concluded that the diameter of the nucleus was about 1/100,000 that of the gold atom.
Copyright©2000 by Houghton Mifflin Company. All rights reserved.