chapter 3 the history of the atom. i. the scientists and their discoveries a.democritus 1. date =...
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Chapter 3
The History of the Atom
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I. The Scientists and their Discoveries
A.Democritus
1. Date = 400 B.C
2. Discovery = Theorized the smallest unit of an
element
3. Importance = gave the term and definition of atom
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Democritus
ATOM
Smallest particle
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B. John Dalton1. Date = 18032. Discovery =
a. Every element is made of atoms
b. atoms of same element exactly the same
c. Atoms of different elements join together to form molecules
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3. Importance = proposed the ATOMIC THEORY
Atomic Theory =
1. everything is made up of atoms
2. atoms make up molecules
3. atoms of the same element are the same
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Molecules made of atoms
John Dalton
Atomic Theory
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C. J.J. Thomson
1. Date = 1898
2. Discovery =
a. discovered electrons
b. electrons are negative
3. Importance =
atoms have both negative and positive particles
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J.J. Thomson
“Plum Pudding” model
Electrons are negative
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D. Ernest Rutherford
1. Date = 1911
2. Discovery =
a. discovered nucleus
b. did a “gold foil” experiment
c. atoms mostly made of space
3. Importance =
a. nucleus is very tiny, and positively charged
b. electrons outside of nucleus
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Ernest Rutherford
Gold Foil Experiment
Electrons outside nucleus
Discovered nucleus
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E. Niels Bohr
1. Date = 1913
2. Discovery =
a. Electrons are in energy levels
b. s, p, d, f orbitals
c. 1st = 2 electrons;
2nd = 8 electrons;
3rd = 18 electrons
4th = 32 electrons
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3. Importance =
electrons orbit around nucleus in a certain pathway
This is the Bohr Model
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Niels Bohr
Electrons in energy levels
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F. Schrödinger1. Date = present 2. Discovery = electrons are
impossible to find ( a moving fan)
3. Importance =a. Atoms are neutralb. atoms must have the same
number of protons and electrons
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Schrödinger
Atoms have no charge
Same number of protons and electrons
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II. The Mass of Atom
A. Protons1. are positively charge2. have a mass of 1.67 X 10-27 kg3. Found in the nucleus
B. Neutrons1. Neutral 2. have a mass of 1.67 X 10-27 kg3. Found in the nucleus
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C. Electrons
1. are negatively charged
2. Have a mass of 9.11 X 10-31 kg = 0 atom mass
3. Found orbiting outside the nucleus, so their mass does not effect the atom’s mass!
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Section Question1. Which scientist gave us the word
atom?2. Which scientist made up the
atomic theory? 3. Every element is made of atoms,
atoms of the same element are exactly the same, different atoms make up molecules. These statements make up the what?
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4. Which scientist discovered the electrons?
5. Which scientist discovered the nucleus?
6. Which scientist discovered that electrons where in energy levels?
7. Which scientist said atoms where neutral because they had equal number of protons and electrons?
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8. What is the mass of protons?
9. What is the mass of neutrons?
10. What is the mass of electrons?
11. Which part of the atom has the least amount of mass?