Chem 125 Lecture 2 9701 Projected material

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Chem 125 Lecture 29/7/01Projected material
This material is for the exclusive use of Chem
125 students at Yale and may not be copied or
distributed further. It is not readily
understood without reference to notes from the
lecture.
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What Lewis Added
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Text p. 16
empirical rules for assessing the relative
importance of the resonance structures of
molecules and ions.
1. Resonance structures involve no change in the
positions of nuclei only electron distribution
is involved.
LORE
2. Structures in which all first-row atoms have
filled octets are generally important however,
resulting formal charges and electronegativity
differences can make appropriate nonoctet
structures comparably important.
3. The more important structures are those
involving a minimum of charge separation,
particularly among atoms of comparable
electronegativity. Structures with negative
charges assigned to electronegative atoms may
also be important.
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Levitator by Martin Simon (UCLA)
Eppur sta fermo
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Earnshaw's Theorem(1839)
In systems governed by inverse-square force
laws there can be no local minimum (or
maximum) of potential energy.
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Visualizing Earnshaw - Coulomb's Electrostatics
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A positive particle has a local maximum or
minimum of energy only at the location of another
charged particle, never in free space.
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Force Laws
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J.J. Thomson (1856-1940)
Electron (1897)