Will stick to isolated, finite molecules (not crystals).

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Will stick to isolated, finite molecules (not
crystals).
SYMMETRY OPERATION
Carry out some operation on a molecule (or
other object) - e.g. rotation. If final
configuration is INDISTINGUISHABLE from the
initial one - then the operation is a SYMMETRY
OPERATION for that object.
N.B. Indistinguishable does not necessarily
mean identical.
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e.g. for a square piece of card, rotate by 90º as
shown below
Labels show final configuration is NOT identical
to original.
Further 90º rotations give other
indistinguishable configurations - until after 4
(360º) the result is identical.
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SYMMETRY OPERATIONS
Motions of molecule (rotations, reflections,
inversions etc. - see below) which convert
molecule into configuration indistinguishable
from original.
SYMMETRY ELEMENTS
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C3 Isle of Man Coat of Arms
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Where is the Isle of Man?
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C3
Picture by MC Escher
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When m n we have a special case, which
introduces a new type of symmetry operation.....
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MORE ROTATION AXES
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Some additional points about symmetry axes
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Reflection
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Mirror Plane
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Greek letter sigma
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C2
sv
sv
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Best described in terms of cartesian axes
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Position of P given by x,y,z
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C2H6
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Summary of symmetry elements and operations
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A collection of symmetry operations all of which
pass through a single point A point group for a
molecule is a quantitative measure of the
symmetry of that molecule
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Ripening C2H4
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HCN Zyklon - B
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HCN in Space - Titan
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SiCl4
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SiF4
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