GSCI 163
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Transcript of GSCI 163
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GSCI 163
Lecture 2
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Atomic theory
• What are things made of?
Imagine dividing an object into smaller and smaller units. Is there a limit to how much we can divide?
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Atom
• Means “uncuttable”. Democritus (460-362 BC)
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John Dalton (1766 – 1844)
• All matter is made of atoms• Atoms cannot be created or destroyed.• All atoms of a given element are identical in
mass and properties. Different elements differ from each other because they are made of different atoms.
• Compounds are formed by the combination of two or more kinds of atoms in precise ratios.
• A chemical reaction is a rearrangement of atoms.
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Is the atom indivisible?
• J.J. Thompson – discovery of the electron 1897.
The cathode ray tube
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What is the electron?
• Robert A. Millikan in 1906 measured the charge of a single electron
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The model of the atom at this point
• Positive and negative charges mixed like raisin in jello
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Discovery of the nucleus
• Ernest Rutherford in 1907 found that the atom has a nucleus made of positive particles.
• 100,000 smaller than the orbit of the electron
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How is the nucleus held together?
• We need a glue to overcome electrical repulsion!
• New particle = neutron
• James Chadwick in 1932
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Dmitri Mendeleev
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Next class
Atomic states
• Read handout day 3• Quiz on these topics (first 10-15 min of class)