1. Atomic Theory
Chapter 11, Section 1

2. Rolling Marbles Lab: Questions for Foldable
We rolled marbles at the object to see when and where they passed straight through, bounced back, or changed directions. This helped us figure out the location, size, and shape of the object.
Scientists shot particles at atoms and observed the same things we did to figure out the internal structure of the atom. This helped them develop a model similar to the idea we had in our heads about our mystery object.
Ask students if they had more time and could aim the marble from all directions if they thought the could have figured out the object’s identity (most will say yes). Tell them scientists had better equipment and exact procedures when they did their experiments.

3. What is a model? Representation of an object or system.
Help visualize things we can’t observe directly.
Can be used to test ideas
Help illustrate theories
Examples:
Cells, atoms
Solar system
Model cars, model rockets

4. = 95!
When we mixed the two liquids the overall volume was less than we expected.
This shows that particles can be different shapes and sizes.

5. Ancient Greeks Aristotle Democritus (440 BC)
What are all things made of? The debate about the nature of matter!
Aristotle
Democritus (440 BC)
Break things apart forever and keep their identity
All things were composed of 4 ‘elements’ (Earth, Air, Fire, Water)
Keep breaking in half - eventually get to something that can’t be broken down (indivisible particle) 
“THE ATOM”
Democritus was a PHILOSOPHER, not a SCIENTIST.
He used reasoning, not experiments to come up with his idea.

6. Ancient Greeks Aristotle Democritus (440 BC)
What are all things made of? The debate about the nature of matter!
Aristotle
Democritus (440 BC)
Break things apart forever and keep their identity
All things were composed of 4 ‘elements’ (Earth, Air, Fire, Water)
Keep breaking in half
Eventually get to something that can’t be broken down (indivisible particle) 
“THE ATOM”
Atoms are small, hard particles made of a single material and formed into different shapes and sizes.
Atoms are always moving.
Atoms form different materials by joining together.
Democritus’s model like a “mini-marble”
Although Democritus is closer to being correct, Aristotle's ideas were more widely accepted.
1800’s  experimental data began to support Democritus

7. Dalton’s Atomic Theory (1803)
1st to provide experimental evidence of atoms.
Experimented with combining elements
Noticed that elements combined in specific proportions
2H + O  H2O (Water is always made of 2 Hydrogen and an Oxygen)
Talk about reaction of hydrogen and oxygen gas to make water. How do we know it is H2O? Tanks filled with hydrogen and oxygen – use for the reaction  hydrogen tank empties first, oxygen tank still half full

8. Dalton’s Atomic Theory (1803)
DALTON SUMMARIZED
Atoms are the smallest particles – they can’t be divided (nothing inside atom)
Atoms of the same element are exactly the same; atoms of different elements are different
Atoms join with other atoms to make new substances (compounds)

9. Thomson’s Experiment (1897)
Used a cathode-ray tube.
Invisible beam would “bend” towards positive side  beam made of negative particles
Discovered electrons
Talk about how cathode-ray tubes were found in the old giant box TVs. Discuss electricity (flow of electrons). Tell students that Thomson inferred that the beam was negative based on his observation that it bent toward the positive plate. BUT, since he knew atoms were neutral overall, this made him think there were positive and negative parts/pieces.

10. Thomson’s Model (1897) Discovered atoms are made of smaller parts.
Since atoms are neutral, they must also have positive particles (to balance the negative ones he discovered).
Proposed Plum-Pudding model or ‘choc chip ice-cream’ model
Ice cream = Positive charges (protons)
Chocolate Chips = Negative charges (electrons)

11. Rutherford (1911)
Gold foil experiment – aimed beam of positively charged particles at thin sheet of gold foil
If atoms were “soft blobs” the particles should pass straight through

12. Rutherford (1911) Only a few particles bounced back 
Atoms have dense positively
charged centers (nucleus)
Most particles passed straight through the foil 
Atoms have lots of empty space.

13. Bohr Model (1913)
Used crazy math tricks to build on Rutherford’s model
Electrons travel in paths (around nucleus) and are found in specific energy levels
Atoms can jump between levels from path to path
Talk about “Solar System model” (electrons in “orbits” like planets, nucleus like sun)
AKA
“Solar System model”
We will use the Bohr model to represent atoms in here

14. Modern Theory – Twentieth Century Scientists
Electrons move unpredictably but spend more time in certain regions than others.
Electron clouds – where electrons are most likely to be found
Click twice to show center graphic. Point out darker regions are places with a higher probability of finding an electron at a given time.

15. Will our model of the atom look the same in another 50 years???
Most likely, the answer is NO!
Theories change over time as new experiments are conducted and new information is acquired.

16. Exit Ticket Write the correct letter(s) for each question below.
A = Aristotle B = Democritus C = Dalton
Scientist
Philosopher
Ancient Greeks
Believed that atoms were the smallest thing.
Reasoned that atoms were the “indivisible particle”.
Used experiments to prove atoms existed.
All things were made of earth, air, fire, or water.
7 = MAS = ADV = MTS = APP = BEG

17. Exit Ticket Write the correct letter(s) for each question below.
A = Thomson B = Rutherford C = Bohr
Gold foil experiment
Crazy math tricks
Cathode ray tube
Discovered the electron
Discovered the nucleus
Plum pudding model
Electrons travel in paths around the nucleus
7 = MAS = ADV = MTS = APP = BEG