Chapter 2'12'4

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Chapter 2.1-2.4 definition of moles

• Atoms, Molecules, and Ions

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Atomic Theory (Dalton)

• Elements are made up of atoms (Na, K, H, etc.)
• Atoms of same elements have same properties
• Atoms are neither created nor destroyed in a
  chemical reaction (Law of Conservation of mass)
• Compounds are formed by combinations of elements
  in fixed ratios.
• H2O ? 2 H, 1 O

3

• What makes an atom?
• How can one get that information?
• What makes an egg?
• How can you get that information?

4

• ATOM
• Electron (e) Proton (p) Neutron (n)
• Charge -1 1
  0
• (au)
• Mass 1/1837 1
  1
• (au)
• 1 amu 1.66 x 10-24 g

5
Discovery Characterization of the electron (e)

• Cathode Ray
• (-) charges
• electrons

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Thompsons Experiment

• With electrically charged plates and a magnet
• Charge/mass ratio for an electron
• (e/m) 1.76 x 108 Coulomb/g (or
• 
  C/g)

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Millikan oil-drop experiment
Charge of e- 1.60 x 10-19 Coulomb (C) Mass of
e- 9.10 x 10-28 g
8
Radioactivity

• Spontaneous emission of radiation
• a ( )
• ß ( ) ? electron
• ? ( ?)
• Note 238 is protons neutrons, 92
  is protons
• a is attracted to (-) plate and hence must
  contain () charge

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Rutherfords Experiment

• Atom
• Protons (p), Neutrons (n), and Electrons (e-)
• How are they together?
• Are they uniformly spread over?

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Rutherfords Experiment

• a-Particles are allowed to strike a gold plate
• Most particles go through
• A few go backward

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Rutherfords Experiment

• Can we predict what is going on in Rutherfords
  Experiment?
• Why do a particles (used as balls) go through
  undeflected?

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Rutherfords Experiment

• Conclusion
• An atom is mostly made up of empty space (like an
  open door) with a massive nucleus (like a
  concrete wall), occupying a very small volume.
• Nucleus has protons and neutrons, electrons
  revolve outside.

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Isotopes, Atomic Number, and Mass Number

• Atomic number Number of Protons
• Mass number Protons
• 
  Neutrons
• Can you define isotopes?
• Same elements?
• How are they different?

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Isotopes, Atomic Numbers, and Mass Numbers

• Here is an example of Isotopes.
• Remember that the top number is the mass and
  the bottom number is the atomic .

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Average Atomic Mass

• Avg. mass P1M1 P2M2
• P1 abundance for Isotope 1
• M1 Mass for Isotope 1
• P2 abundance for Isotope 2
• M2 Mass for Isotope 2
• Refer to Problem 29 (Pg. 72)

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Mass Spectrometer

• Obtain atomic and molecular weights
• Need gaseous samples
• Ionization of sample by high energy electrons
• Pass gaseous ions through poles of a magnet
• For ions carrying the same charge, more massive
  particles will be less deflected than the less
  massive particles. Thus, mass separation takes
  place.

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Mole Number

• 1 thousand 103 1000
• 1 million 106
• 1 mole 6.022 x 1023 (Avogadros number)
• 1 mole H atoms 6.022 x 1023 H atoms
• 1 mole H2O molecules 6.022 x 1023 H2O molecules

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Mole Gram (Molar Mass)

• (Remember M-g-P mole-gram-Periodic Table)
• 1 mole C weighs 12.0107 g 12.0 g C atoms
• Found on the Periodic Table
• 1 mole H weighs 1.00794 g 1.00 g H atoms
• 1 mole H2O 2(1.00794) 15.9994 2 16 18 g
  H2O molecules

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