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Robert Boyle
provided evidence for the atoms and defiend the nature of an element
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Joseph Priestley
isolated oxygen gas from decomp of mercury oxide
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Antoine Lavoisier
showed that mass of products is exactly equal to the mass of reactants
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Law of Mass Conservation
Mass is neither created nor destroyed in chemical reactions
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Law of Definite Proportions
Different samples f a pure chemical substance always contain the same proportion of elements by mass
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by mass, water is __.
- 88.8% oxygen
- 11.2% hydrogen
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John Dalton
proposed explanations for the laws of mass conservation adn definite proportions
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Dalton's Postulates
- I. Elements are made of tiny particles called atoms.
- II. Each element is characterized by the mass of its atoms. Atoms of the same element have the same amss, but atoms of different elements have differnet masses.
- III. Chemical combination of elemetns to make differnet substances occurs when atoms join together in small whole-number ratios.
- IV. Chemical reactions only rearrange the way that atoms are combined; the atoms themselves are unchanged.
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Law of Multiple Proportions
ex: Nitrogen and oxygen combine to form NO and NO2.
In NO, the N:O mass ratio is __.
In NO2, the N:O mass ratio is __.
- When two elements form two different compounds, the mass ratios are related by small whole numbers
- 7:8
- 7:16
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What did the Cathode-Ray tube by Thomson propose?
- that cathode rays must consist of timy - charged particles
- (electrons)
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Deflection of electron depends on three factors:
1) ?
2) ?
3) ?
- 1) Strength of electric or magnetic field
- 2) Size of negative charge on electron
- 3) Mass of the electron
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What did the Oil Drop Experimetn by Millikan determine?
the mass of an electron
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Explain the Oil Drop Experiment?
- Applied a voltage to oppose the downward fall of charged drops and suspend them
- voltage on plates place a charge on each oil drop, and are suspended between two electrically charged plates
- The experiment calculated the electrons' mass
-
What did Rutherford discover? How?
- nucleus
- irradicated gold foil with a beam of alpha particles to search for positively charged particles
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Mass #
# of protons plus neutrons
-
Atomic #
# of protons or electrons
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Isotopes
What are the three
- atoms with identical atomic #s, but different mass numbers
- Protium
- Deuterium
- Tritium
-
Protium
- one proton and no neutrons
- mass #= 1
-
Deuterium
- one proton/ one neutron
- mass #= 2
-
Tritium
- one proton and two neutrons
- mass number= 3
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Average Isotopic Mass
weighted avg. of teh isotopic masses of an element's naturally occurring isotopes
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Atomic mass
a weighted average of the isotopic masses of an elemetn's naturally occurring isotopes
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