Chapter 2: Modern Atomic Theory

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Chapter 2 Modern Atomic Theory

• Matter consists of atoms
• Atoms consist of three fundamental particles,
  found in the nucleus and the space around the
  nucleus

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Arrangement of Subatomic Particlesnot to scale!
Nucleus contains protons and neutrons.

• If an atom has a diameter of about 100 m (a
  football field), the nucleus would be 1 mm in
  diameter

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What holds an atom together?
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What holds an atom together?
Coulombs Law of electrostatic interactions.
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What holds an atom together?
Coulombs Law of electrostatic interactions.
General Behavior Like charges
repel. Opposite charges attract.
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What holds an atom together?
Coulombs Law of electrostatic interactions.

• If we double a charge from 1 to 2, the force
  will
• Double
• Halve
• Quadruple
• Quarter

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What holds an atom together?
Coulombs Law of electrostatic interactions.

• If we double the distance, the force will
• Double
• Halve
• Quadruple
• Quarter

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Whats wrong with this picture?
Electrons are held near the nucleus by the
electrostatic attraction between them, but
The forces of nature
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Were not just making it up!

• How could we possibly know that the nucleus
• is small compared to the size of the atom?
• Why not think the protons, electrons and neutrons
  are all mixed together?

The Rutherford Experiment
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Were not just making it up!
The Rutherford Experiment
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Were not just making it up!
The Rutherford Experiment
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Atom Terminology

• All atoms of an element have the same atomic
  number number of protons
• In a neutral atom (no charge), the number of
  positively and negatively charged particles must
  be equal.
• Number protons number electrons
• The mass number protons neutrons

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Isotopes

• Isotopes are atoms of an element with the same
  number of protons but different numbers of
  neutrons, and different mass
• Atom symbols are written using the following
  format X symbol of element A mass
  number Z atomic number

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Isotopes, continued

• Most elements have multiple isotopes
• 1H, 2H (deuterium), 3H (tritium, radioactive)
• 79Br, 81Br
• 64Zn, 66Zn, 67Zn, 68Zn, 70Zn
• While atomic mass is the mass of an atom,
  average atomic mass takes into account isotopes
  and natural abundance
• We use atomic mass units (amu)1 amu 1.661 x
  1024 g(about the mass of a proton)

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WHAT TIME IS IT?

• Puppy
• Dog
• Isotopes

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Chiuaua 4 lbs.
Mastif 120 lbs.
What is the average weight of a collection of
these dogs?
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(No Transcript)
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• 96 Chiuauas _at_ 4 lbs.
• 4 Mastifs _at_ 120 lbs.

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Isotopes and Average Atomic Masses
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Isotopes and Average Atomic Masses
Example Boron
B has 2 isotopes B-10 mass 10.0129 amu
abundance 19.91 B-11 mass
11.0093 abundance 80.09
What is the average atomic mass of Boron?
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What time is it?
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HOW
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HOWDO
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HOWDOYOU
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HOWDOYOUKNOW
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HOWDOYOUKNOWTHAT?
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Mass Spectrometry
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Isotopes In The News
http//www.nytimes.com/2007/08/21/science/21mari.h
tml?ex1188705600en7d1e0dc4064c4cfeei5070
http//www.nytimes.com/2007/04/24/sports/otherspor
ts/24landis.html?ex1188705600en1241fcb09b9c265c
ei5070