1. Catalyst – February 2 3 – 6, 2010 HOMEWORK OUT PLEASE! Write a sentence describing what a theory is. Why weren’t cell phones invented when regular phones were?

2. Today’s Agenda  Catalyst  Unit 1 Tracking  Atomic Theory Part 1  Exit Question

3. Today’s Objectives  SWBAT describe the evolution of the atomic theory from 420 B.C. to 1898.  SWBAT defend a conclusion using research as evidence.

4. What is an atom? Key Point #1: An atom is the smallest part of an element that retains (keeps) the properties of the element

5. Well then, what is an element? Key Point #2: An element is a pure substance that cannot be broken down into simpler substances by physical or chemical means NOT THIS KIND OF ELEMENT

6. Well then, what is an element? Key Point #2: An element is a pure substance that cannot be broken down into simpler substances by physical or chemical means NOT THIS KIND OF ELEMENT

7. Well then, what is an element? THESE KINDS OF ELEMENTS

8. Why is the atom so important? The atom is the building block of all matter! Without atoms, our universe would no exist!

9. Essential Questions for Unit 2 1) What are the most important contributions to the development of atomic theory? 2) What makes one atom different from another? How are atoms similar? 3) Why is it so important to understand how the periodic table is organized? 4) What secrets can we uncover about the elements using the periodic table?

10. Atomic Theory  Atomic theory is the theory we will focus on in Chemistry  It is theory of the nature of matter (stuff)  Tells us that all matter is composed of atoms  The specifics of the theory have change a lot  Why is atomic theory considered a theory instead of a fact?  Why do you think the theory changed throughout history?

11. Major Playas of Atomic Theory Democritus (460-370 B.C.) John Dalton (1808) J.J. Thomson (1897) Ernest Rutherford (1909) Niels Bohr (1913) Schrodinger (1924)

12. In the beginning…  Around 420 B.C. Democritus, a Greek philosopher, was the first to think of the idea of atoms  A philosopher is a thinker  Around the same time Aristotle, a more famous philosopher, proposed a different idea.

13. What were Democritus’ ideas? Matter is composed of tiny particles called atomos Different kinds of particles have different sizes and shapes Particles move through empty space

14. In the beginning…  Aristotle gave us this quote…  Among other things…  He challenged the ideas of Democritus  He did not think the “nothingness” of empty space could exist “We are what we repeatedly do. Excellence, therefore, is not an act but a habit.”

15. Questions to Ponder…  Why was Democritus’ idea not a theory?

16. Then came along…  In 1808, John Dalton came up with the first atomic theory that was based on scientific research.  It stated:  1) All matter is made of atoms.  2) Atoms are indivisible and indestructible.  3) All atoms of a given element are identical in mass and properties  4) Compounds are formed by a combination of two or more different kinds of atoms.  5) A chemical reaction is a rearrangement of atoms.

17. What were Dalton’s conclusions? Atoms are hard, round, solid balls. They are similar to marbles.

18. Questions to Ponder…  Why would people believe John Dalton and not Democritus?  What makes John Dalton’s ideas about the atom a theory and Democritus’ ideas a thought?

19. But Dalton Was Wrong! (kind of)  In 1897, J.J. Thompson performed the Cathode Ray Experiment  Shot a beam of electrons from one end of a tube to the other

20. Thompson’s Hypothesis  Thompson hypothesized that:  The beam went from the negative side to the positive side. Since opposites attract the particles must be negative

21. Thompson’s Conclusions  Atoms have parts of them that are negatively charged  Scientists knew from before that atoms are neutral (no charge)  Question to Ponder…  What other piece of information can scientists infer about atoms based on the above information?

22. The Old Theory  Recall Part 2 of John Dalton’s Atomic Theory  2) Atoms are indivisible and indestructible.  Question to Ponder…  How did J.J. Thompson’s Experiment affect this part of the Atomic Theory?

23. Theories and Evidence  When evidence is found that does not support a theory, the theory has to be modified to include the new evidence  A new theory must be made

24. J.J. Thompson’s New Model  The new model was called the Plum Pudding Model  Plum pudding is like raisin oatmeal  The negative particles floated in a sea of positive charge like raisins in oatmeal Plum Pudding Model Dalton’s Model

25. Thomson is so hood… Now I have finished my model! It looks like Plum Pudding!

26. Classwork/Homework  Classwork: Read and create a 1 page outline for the following pages in your textbook:  65-67 (Democritus and Dalton)  70-71 (JJ Thompson)  Homework:  Answer all the questions on the half sheet of paper Look in your notes and your book for clues

27. Exit Question 1. Why was Dalton’s theory of the atom more believable than Democritus’? 2. What did Thomson discover to dramatically change the theory of the atom?