NUCLEAR CHEMISTRY

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HISTORY of the Atom
Atomic ModelDevelopment
Rev 6/7/06
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Early Philosophers
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Democritus (460-370 BC)

• Defined an Atom as the smallest unit of a
  material that can not be split up
• Greek word atom
• means invisible

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Democrituss Theory

• Matter is made up of empty space through which
  atoms move.
• There is an indestructible and indivisible
  particle called the atom.
• Different atoms have different sizes and shapes.
• Different properties are related to the size and
  shape of the atoms.

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John Dalton (1766 1844)

• Revised Democrituss theory of the atom making
  Daltons atomic theory.
• Atom smallest particle of an element that still
  retains the properties of that element.

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Daltons Postulates - 1807

• All matter is made of atoms

• Atoms of same element are the same. If it is a
  different element, the atoms are different

• Atoms can not be created or destroyed but can be
  combined, rearranged, or separated.

• Atoms form in simple whole number
• ratios to form compounds.
• Example H2O water is always found in a 21
  ratio

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The History of Subatomic Particles

• William Crookes Invented cathode-ray tube

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JJ Thomson (1856- 1940)

• Used cathode ray tube to perform experiments
  using magnets and observing what effect the
  magnets had on the ray within the tube

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Thomsons Atom - 1897

• Discovered electrons are smaller than a Hydrogen
  atom
• Plum Pudding model of atom

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Robert Millikan (1868 1909)

• Oil Drop Experiment
• Determined Charge of Electron (-1)
• Determined Mass of Electron 1/1840th that of
  Hydrogen

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The Nuclear Atom

• Rutherford (1871- 1937)

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Rutherfords Gold Foil Experiment

• Performed and discovered by YOU!!!
• End Conclusions
• 1)
• 2)

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James Chadwick

• Additional mass of nucleus must be made up by a
  neutral particle known as
• the neutron

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Structure of an Atom
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Nucleus

• responsible for most of the mass of the atom
• protons ( charge)
• neutrons (no charge)

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Electrons

• (-) charge
• responsible for most
• of the volume of the
• atom
• negligible mass (0)

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Determining P, N, and E

• Atomic Number The number of protons in an atom.
  
• In a neutral atom Number of protons number of
  electrons
• Mass Number
• protons neutrons
• of Neutrons
• atomic mass protons

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Isotopes

• Kind of like twinsalike, but different
• Isotopes -Same element, but with different mass
  due to different of neutrons
• Same number of protons

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Isotopes can be written 2 ways
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1. Nuclear Notation
neutrons protons--gt

• mass --gt
• lt--element Symbol
• atomic --gt

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K
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protons--gt
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2. Hyphen Notation

• Hyphen notation looks like this
• C-12 C-14
• The number after the hyphen mass number
  (atomic mass) Carbon
• So what does that mean?

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Practice (Neutral Atoms)
Protons Electrons Neutrons
Silicon - 30
18O
He - 5
29 35
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Average Atomic Mass

• Average Atomic Mass The average of all
  naturally occurring isotopes.

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• Uranium has three common isotopes. If the
  abundance of 234U is 0.01, the abundance of 235U
  is 0.71, and the abundance of 238U is 99.28,
  what is the average atomic mass of uranium?

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• Titanium has five common isotopes 46Ti (8.0),
  47Ti (7.8), 48Ti (73.4), 49Ti (5.5), 50Ti
  (5.3). What is the average atomic mass of
  titanium?

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Isotopic Abundance

• Nitrogen is made up of two isotopes, N-14
  (14.00307) and N-15 (15.0001). Given nitrogen's
  atomic weight of 14.007, what is the percent
  abundance of each isotope?

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• Copper is made up of two isotopes, Cu-63 (62.9296
  amu) and Cu-65 (64.9278 amu). Given copper's
  atomic weight of 63.546, what is the percent
  abundance of each isotope?

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• Lithium has 2 natural isotopes, Li6 and Li7. they
  have atomic masses of 6.0151amu and 7.0160amu
  respectively, which isotope would be found in
  greater abundance?

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Bohr and Lewis

• Bohr Model A planetary model of the atom with
  electrons orbiting the nucleus
• Lewis Dot Structure model representing the
  valence electron pattern across the periodic
  table
• Valence Electron electron in the outermost
  shell/energy level

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Bohrs atom - 1913
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Drawing Bohr Models

• Electrons are arranged in Energy Levels or Shells
  around the nucleus of an atom.
• - first shell a maximum of 2 electrons
• - second shell a maximum of 8 electrons
• third shell a maximum of 8 electrons
• fourth shell a maximum of 2 electrons