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provided evidence for the atoms and defiend the nature of an element
isolated oxygen gas from decomp of mercury oxide
showed that mass of products is exactly equal to the mass of reactants
Law of Mass Conservation
Mass is neither created nor destroyed in chemical reactions
Law of Definite Proportions
Different samples f a pure chemical substance always contain the same proportion of elements by mass
by mass, water is __.
- 88.8% oxygen
- 11.2% hydrogen
proposed explanations for the laws of mass conservation adn definite proportions
- 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.
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
What did the Cathode-Ray tube by Thomson propose?
- that cathode rays must consist of timy - charged particles
Deflection of electron depends on three factors:
- 1) Strength of electric or magnetic field
- 2) Size of negative charge on electron
- 3) Mass of the electron
What did the Oil Drop Experimetn by Millikan determine?
the mass of an electron
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?
- irradicated gold foil with a beam of alpha particles to search for positively charged particles
# of protons plus neutrons
# of protons or electrons
What are the three
- atoms with identical atomic #s, but different mass numbers
- one proton and no neutrons
- mass #= 1
- one proton/ one neutron
- mass #= 2
- one proton and two neutrons
- mass number= 3
Average Isotopic Mass
weighted avg. of teh isotopic masses of an element's naturally occurring isotopes
a weighted average of the isotopic masses of an elemetn's naturally occurring isotopes