do now work silently. raise hand to ask ms. hughes anything. 1.what is an atom? 2.describe...
TRANSCRIPT
Do nowWork 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 TheoryDemocritus (460-370 B.C.)
Aristotle (384-322 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!
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 THANONE 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 (1766-
1844)
•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 (1856-1940)
•Experiment: Cathode ray tube
•When: 1898
•Where: England
Thomson’s Cathode Ray Tube
Quick! Reading Time!
• Pages 92-93
• 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 CONCLUSI
ONS
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 TimeR = Role
Pretend to be either Dalton or Thomson.A = Audience
You are writing to inform everyone of your discoveries!
F = FormatLetter, Newspaper column, cartoon, or rap/poem
T = TopicDetails 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?