1. Atomic Theories
Page 53 of INB

2. How are Democritus and Daltons atomic theories similar?
Essential Question:
How are Democritus and Daltons atomic theories similar?

3. First introduced the idea of the atom.
Democritus (400 BC)
First introduced the idea of the atom.
Atom: unable to divide.
No real evidence to support his theory
Was just an explanation for his observations.

4. Dalton (1808):
All matter (elements) is composed of extremely small atoms
All atoms are specific to each element; same element means atoms have same size, mass, chemical properties
Atoms can’t be subdivided, created, or destroyed
Atoms of one element can combine with atoms from another element in whole # ratios to form chemical compounds (law of definite proportions).
Chemical reactions can combine, separate or change the atoms arrangement

5. JJ Thompson (1897): Studied electricity using cathode ray tube.
Cathode rays have a negative charge, independent of gas used.
If the ray was attracted to the positive side and repelled by the negative side. The particles must be negatively charged.
Proved the atom must contain negative particles (electrons).
Plum pudding model of the atom.

7. Rutherford (1911):
Gold foil experiment: Most alpha particles passed through undisturbed BUT some were deflected
If the particle went straight through, it did not come in contact with anything.
Since, most went straight through the atom is mostly empty space.
New model positive charged middle with electrons around the outside.

10. Atomic theories review questions: Page 52
1) Describe Democritus’s theory. 2) Summarize Dalton’s theory. 3) Why was Dalton’s theory more accepted then Democritus’s? 4) Compare Daltons atomic theory and Rutherford's atomic theory. 5) How did the cathode ray tube experiment lead to the discovery of electrons. 6) How did the gold foil experiment lead to the discovery of the nucleus? 7) Does the term indivisible still describe the atom? Explain.

11. Atomic theories review questions: Page 52
1) Describe Democritus’s theory. 2) Summarize Dalton’s theory. 3) Why was Dalton’s theory more accepted then Democritus’s? 4) Compare Daltons atomic theory and Rutherford's atomic theory. 5) How did the cathode ray tube experiment lead to the discovery of electrons. 6) How did the gold foil experiment lead to the discovery of the nucleus? 7) Does the term indivisible still describe the atom? Explain.