1. Platinum and Nickel
How did we get here?
Copper Atoms
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Blue- tin
Red- silicon
Green- lead
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Carbon atoms

2. ATOMIC THEORY
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3. Scientists Cat Joke Democritus & Leucippus John Dalton Ancient Greeks
J.J. Thomson
Ernest Rutherford
Niels Bohr
Summary Video
Atom Review
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4. Cat Joke!
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5. Ancient Greeks (450 BC) Believed all matter was made of: Earth Fire
Water
Air
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6. Cat Joke!
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7. Democritus & Leucippus (300 BC)
Experimental Conclusions
Experiment
New
Model
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8. Democritus & Leucippus
Experiment
They did not run any experiments.
Atoms were an invention of their minds
Democritus & Leucippus
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9. Experimental Conclusions
Atoms are the smallest particles of matter
Defines the atom as the smallest particle
Explains the existence of elements
Democritus & Leucippus
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10. Democritus & Leucippus
Model
Name:
Atom the indivisible particle
Description:
Matter is made up of particles so small and indestructible that they cannot be broken down into smaller units- particles were called “atomos”, which is Greek from “indivisible”
Democritus & Leucippus
Model Shortcomings

11. Democritus & Leucippus
Model Shortcomings
No scientific view of the atom only a conceptual definition
Does not talk about subatomic particles (electrons, protons, neutrons)
Democritus & Leucippus
Cat Joke!

12. Democritus & Leucippus
Cat Joke!
Democritus & Leucippus
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13. Experimental Conclusions
John Dalton (1800)
Dalton Fun Facts 
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Experiment
Experimental Conclusions
New
Model
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14. Experiment
Dalton ran experiments with different types of gases and through deductive reasoning and experimentation he came to several conclusions.
Dalton
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15. Experimental Conclusions
Pure Elements consist of particles called atoms.
Atoms of an element are all the same for that element. That means gold is gold and oxygen is oxygen down to the last atom.
Atoms of different elements can be told apart by their atomic weights.
Atoms of elements unite to form chemical compounds.
Atoms can neither be created or destroyed in chemical reaction.
Dalton
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16. Dalton’s Model Model Shortcomings Name: The Solid Sphere Model
(Clay Ball Model)
Description:
Atoms are seen as solid, indestructible spheres (like billiard balls)
Dalton
Model Shortcomings

17. Model Shortcomings
Atoms are not indivisible (b/c they are made up of subatomic particles)
Atoms can change from one element to another by radioactive decay (not by chemical reactions).
Not all atoms of the same element have exactly the same mass (isotopes).
Dalton
Cat Joke!

18. Cat Joke!
Dalton
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19. Experimental Conclusions
J.J. Thomson (1850)
Experimental Conclusions
Experiment
New
Model
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20. Experiment Experiment Animation Next
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21. Summarized Experiment
Detailed explanation of cathode ray tube
Voltage
Cathode
(-)
anode
(+)
Click here
Empty glass tube (vacuum) connected to a metal cathode and anode.
High voltage is applied to the tube.
This caused the atoms in the cathode to get excited.
Electrons stream off the cathode, producing a cathode ray.
The cathode ray traveled toward the anode
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22. Summarized Experiment
Voltage -
Cathode
(-)
anode
(+)
Click here
When a negative charge was brought toward the cathode ray, it caused the cathode ray to move away from the negative charge.
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23. Summarized Experiment
Voltage +
Cathode
(-)
anode
(+)
Click here
When a positive charge was brought toward the cathode ray, it caused the cathode ray to move toward the positive charge.
Thomson
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24. Experimental Conclusion
Discovered the electron
Electrons have negative charges
Electrons are evenly distributed in a positive sphere.
Thomson
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25. Thomson’s Model Name: Plum Pudding Model Description:
Atoms are solid spheres made up of a solid positive mass with tiny negative particles embedded in the positive core.
Like a chocolate chip cookie!
Cookie is positive
Chocolate chips are negative electrons
Thomson
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26. Real Plum Pudding! Gross!!
Thomson
Model Shortcomings

27. Model Shortcomings
Does not explain the existence of electrons outside the nucleus
Does not explain the role of electrons in bonding
Does not talk about neutrons, protons, or the nucleus
Thomson
Cat Joke!

28. Cat Joke!
Thomson
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29. Experimental Conclusions
Ernest Rutherford (1905)
Experiment
Experimental Conclusions
New
Model
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30. Experiment Experiment Animation Next
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31. Summarized Experiment
Sent alpha particles (+2 charged Helium atoms) at a thin layer of gold foil
He expected 100% of the particles to go through to screen
90% went through the foil to screen, but 10% were deflected
He was surprised and wrote that this result was comparable with shooting a bullet at a piece of paper and having the shell reflected back.
The plum pudding model could not be correct.
Rutherford
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32. Experimental Conclusion Detailed explanation of gold foil experiment
Atoms are mostly empty space
Atoms have a dense center with a positive charge called a nucleus
Electrons move around the nucleus at a distance
Detailed explanation of gold foil experiment
Rutherford
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33. Rutherford’s Model Model Shortcomings Name: Nuclear atom Description:
Positively charged nucleus in center of atom
Electrons moving around nucleus at a distance
Nucleus
Electrons
Rutherford
Model Shortcomings

34. Model Shortcomings
It does not explain: how negatively charged electrons keep from crashing into the positively-charged nucleus.
Rutherford
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35. Cat Joke!
Rutherford
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36. Experimental Conclusions
Niels Bohr (1920)
Experiment
Experimental Conclusions
New
Model
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37. Experiment Experiment Animation
An important experiment was the study of the emission of light by excited hydrogen atoms.
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38. Experiment Summary
Bohr
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When atoms receive energy, electrons move way from nucleus (higher energy level)
When atoms release energy, electrons move toward nucleus (lower energy level) and release light
Click for examples
Energy Added
Energy Released e-
The resulting hydrogen atoms are excited; that is, they contain excess energy, which they release by emitting light of various wavelengths to produced emission spectrum of the hydrogen atom. e-
Absorbs energy
Releases energy

39. Experimental Conclusion
Electrons can only exist on definite energy levels that are specific distances from the nucleus.
Bohr
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40. Bohr’s Model Model Animation Name: Planetary Model Description:
Positively charged nucleus in center of atom
Electrons moving around nucleus at specific energy levels (or distances from nucleus)
Model Animation
Bohr
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41. Summary of Atomic Theory
Summary Animation
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Atom Review

42. Na Atom Review +1 23 11 Mass number = #protons + # neutrons
Atomic number = #protons= element
Charge= #protons - # electrons
Charge Na +1 23 11
Mass Number
Atomic Number
Nuclear symbol
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43. C C C C Atom Review Mass number = #protons + #neutrons
Average atomic mass = percent abundances of all the isotopes of an element 12 C 13 C 14 C
The average atomic mass is on the periodic table: C
12.01
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44. Sample Average Atomic Mass Calculation
Determine the average atomic mass of Ar if the isotopes are: 5% 79Ar and 95% 80Ar
Step 1: convert % to decimal
0.05 and 0.95
Step 2: multiply decimal by mass number
0.05 X 79 = 3.95
0.95 x 80 = 76
Step 3: add values together
= 79.95
Step 4: check that the value matches the value shown under Ar on the periodic table
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