Download Atomic Theories and Scientists Notes

Law of Conservation of Mass
• Who: Antoine Lavoisier
• Matter can't be created or destroyed
• When: 1785
• Where: France
Law of Definite Proportions
• Who: Joseph Proust
• Compounds – Elements put together in
fixed ratios
C + O2  CO2
• When: 1797
• Where: France
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Law of Multiple Proportions
• Who: John Dalton
• Two elements form more than one compound
between them
• The ratios of the masses of the second element
which combine with a fixed mass of the first
element will be small whole numbers.
• Where: England
When: 1803
Historical Perspectives
Aristotle (350BC) in Greece
•Everything was fire, earth, air, or water
•No smallest part of matter
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Historical Perspectives
Democritus (400 BC) in Greece
•Atoms = smallest unit of elements
•Atomos = indivisible/uncuttable
John Dalton
Solid Sphere Model (1805) in England
Developed an atomic theory
•Elements were made up of atoms
•Each element was composed of the same kind of atoms.
•Different elements were composed of different kinds of
atoms.
•Compounds are composed of atoms in specific ratios.
•Atoms are not created or destroyed in a reaction.
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Problems with Dalton’s Atomic Theory?
1. Matter is composed of indivisible particles
Atoms Can Be Divided, but only in a nuclear
reaction
2. All atoms of a particular element are identical
Does Not Account for Isotopes (atoms of the same
element but a different mass due to a different
number of neutrons)!
3. Different elements have different atoms
YES!
4. Atoms combine in certain whole-number ratios
YES! Called the Law of Definite Proportions
5. In a chemical reaction, atoms are merely rearranged
to form new compounds; they are not created,
destroyed, or changed into atoms of any other
elements.
Yes, except for nuclear reactions that can change
atoms of one element to a different element
J.J. Thomson
What:
Atoms aren't smallest particle
Conducted experiment with a Cathode
Ray Tube
Particles had a negative charge
Model = plum pudding
When: 1897
Where: England
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Cathode Ray Tube
Robert Millikan
What: Experiments to determine mass of electron
Conducted the oil drop experiment
Verified that electron is negatively charged
No new model
Where: America
When: 1910
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Millikan
Oil Drop Experiment
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Ernest Rutherford
• Conducted Gold Foil experiment
• Proved nucleus is dense, positively charged core of
atom
Model = Mass Centered/
Stationary Planetary Model
• When: 1911
• Where: America
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Rutherford’s experiment.
Run video
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Niels Bohr
• What: Pulsating Planetary Model
• Electrons can move between energy levels
• When: 1913
• Where: Denmark
Erwin Schrodinger
• Electron have dual wave-particle nature
• Foundation for quantum theory
• Model = Pulsating orbitals
• Math was used to predict path of the electron
• When: 1926
• Where: Switzerland
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James Chadwick
• Confirmed existence of neutron
• No new atomic model
• When: 1932
• Where: England
The Atom
An atom consists of a
• nucleus
–(of protons and neutrons)
• electrons in space about the nucleus.
Electron cloud
Nucleus
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ATOMIC COMPOSITION
• Protons (p+)
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic mass units (amu)
but we can round to 1 for mass.
• Electrons (e-)
–
negative electrical charge
– relative mass = 0.0005 amu
but we can round to 0 for mass.
• Neutrons (no)
no electrical charge
– mass = 1.009 amu but we can round to 1 for
mass.
–
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