Do now Work silently. Raise hand to ask Ms. Hughes anything. 1.What is an atom? 2.Describe Democritus’s atomic model.

Announcements Unit 3 test next Friday If you have not taken 2 chemistry tests yet this semester, see me after to arrange a make up

Mystery Element #1: Too little of this element in the body causes osteoporosis. #2: You can get this element from drinking milk #3: It is good for your bones!

What to look forward to –We’ll see how scientists figured out that matter is made of atoms when even though they could not see atoms –What all the stuff on the periodic table means –We’ll see how ideas become theories –We’ll see how great scientists were wrong

What is an atom? An atom is the smallest particle of matter that still keeps the identity of a substance. Beaker of Gold (Au)

What is an atom? An atom is the smallest particle of matter that still keeps the identity of a substance. atom Beaker of Gold (Au)

Big Players in Atomic Theory Democritus ( B.C.) Aristotle ( B.C.) John Dalton (1808) J.J. Thomson (1898) R.A. Millikan (1909) Ernest Rutherford (1909) Niels Bohr (1913) Chadwick (1932) Schrodinger (1936)

Challenge Time How does it feel to be one of those scientists, investigating the structure of atoms??? Draw a picture of how you think the tube is constructed. What’s the right answer?

Sorry… Scientists can’t open up atoms to “see if they are right” They just have to keep doing experiments and adding the evidence together If enough evidence adds up, if enough experiments are REPRODUCED we have a THEORY Until new evidence comes along to revise, support, or reject it

Democritus - Conclusions Matter is composed of tiny INDIVISIBLE (can’t be broken down) particles Different kinds of particles have different sizes and shapes Particles move through empty space Page 88

1)Democritus 420 B.C, Greece - Matter is made of “tiny, indivisible particles”, called atoms and empty space. No experiments. REJECTED!

What is a conclusion? Duh! A conclusion is a judgment based on information obtained in an experiment

What is a scientific theory? A scientific theory is not just a hunch! –Explanation of observations –Has been supported by many, many experiments –Can be disproved or modified with new evidence

How is a THEORY different from a HYPOTHESIS? HYPOTHESIS Tentative explanation based on observations ONE SCIENTIST Experiments must still be conducted to test hypothesis I THINK I have an idea!

How is a THEORY different from a HYPOTHESIS? THEORY Explanation supported by many, many experiments MORE THAN ONE SCIENTIST Takes time!

What is a scientific law? A scientific law describes natural phenomena but does not explain why they happen –Can use laws to predict –Foundation of scientific discovery – theories and understanding based on laws

Examples Kepler’s Law of Planetary Motion Law of Gravity Law of Conservation of Matter Theory of Evolution Theory that the Earth was flat Atomic Theory

Coming in Third… John Dalton ( ) Experiment: Careful chemical measurements Where: England When: 1803 Page 90

Four Postulates All matter is made of tiny particles called atoms. All atoms of a given element are identical, but they differ from those of any other element.

Four Postulates Compounds are formed by a combination of 2 or more types of atoms. Chemical reactions occur when atoms are rearranged.

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

Inquiry- There are no right answers here! 1.Positive and negative charges _______ 2.+ and + charges ________ 3.- and – charges ________ 4.Imagine you shot a positive particle through a tunnel. The top of the tunnel is positive; the bottom is negative. What happens to the particle you shot? 5.Imagine the same scenario, but you are shooting a negative particle. What happens? 6.Imagine the same scenario, but you are shooting a neutral particle. What happens?

Cuatro! J. J. Thomson ( ) Experiment: Cathode ray tube When: 1898 Where: England

Thomson’s Cathode Ray Tube Electrons are NEGATIVE!

Thomson’s Cathode Ray Tube Quick! Reading Time! Pages Stop at “The next significant development….”

So what does this mean about the nature of atoms? It was known that all matter was neutral (no positive or negative charge) So if the electron is negative, then what does that mean about the rest of the atom?

He said the atom is a ball with electrons floating around in a sea of positive space Atoms can be divided into smaller SUBATOMIC particles! Thomson’s CONCLUSIONS

Thomson’s Conclusions Now I can finish my model! It looks like Plum Pudding! Or like a chocolate chip cookie!

Ms. Hughes’s version of the cathode ray tube Pay attention! Hypothesis: Materials: water, balloon, hair Procedure: 1. create static on balloon 2. hold balloon to water stream Observations: Conclusion:

Work Time On your own paper, compare and contrast the theories of Democritus, Dalton and Thomson How did each theorist add to or reject the discoveries or ideas developed before him? What experimental evidence was used? Write at least 2 paragraphs (5 sentences or more) Include picture of each theorist’s model.

RAFT - Independent Work Time R = Role Pretend to be either Dalton or Thomson. A = Audience You are writing to inform everyone of your discoveries! F = Format Letter, Newspaper column, cartoon, or rap/poem T = Topic Details of your discovery and how you know it is true - YOU HAVE “WORKED” HARD…DEFEND YOUR RESEARCH! You may use a chemistry book to help.

Exit Slip 1.What experiment did Thomson use? 2.What did he prove? 3.How did that change the atomic model? HW: copy the question, bring answer tomorrow –Make it a QUALITY short answer –What experimental evidence supported the plum pudding model and rejected Dalton’s model? Explain the experiment. Top Ten: how’d we do?