Ask A Scientist Chemistry Archive

name         Monica
status       other
grade        other
location     CT

Question -   Why is molecular geometry so important?
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Good Day,

Molecular Geometry of a compound can be predicted based on the 
elements present, the coordination number and the orbital 
hybridization.  The Molecular Geometry of the compound can be used 
to help make predictions about crystal structures, dipole moment, 
reactivity, bond lengths and angles.  The Molecular Geometry can be 
used to determine specific symmetry elements present, which in turn 
can predict IR and Raman bending or stretching modes which can help 
verify, spectroscopically, the structure of the compound of 
interest.  Molecular geometry can also help the scientist visualize 
reactions of interest, reaction pathways, products or means of 
improving on the reaction of interest.  The Molecular Geometry of 
well characterized compounds can be utilized in the efforts to 
explore new analytical spectroscopic techniques.

A strong understanding of Molecular Geometry can significantly help 
the Chemist.

Fred Boeheim
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Monica,

At a molecular level, there are three things that control chemical 
reactions: (1) rate of collisions - how often the molecules come 
into contact, (2) the orientation of those collisions - whether the 
molecules come into contact in the right locations on the molecule, 
and (3) energy of those collisions - whether when the molecules come 
into contact that the energy is appropriate for a reaction to take 
place. #2 should indicate to you that the shape of a molecule is -in 
a very general way- a factor in the rate of chemical reactions.

We can go into more specifics such as: (a) if a molecule's reactive 
site is blocked by other parts of the molecule, then the molecule is 
not very reactive, (b) if a molecule is of a particular shape and 
will react only with other molecules of a specific shape - the way a 
left hand will only fit well into a left-handed glove, (c) if the 
target product will only come out from a specific starting shape 
-sort of like, you can only expect to get a left handed glove off of 
a left hand, etc. ---but all of these go back to #2 above.

Greg (Roberto Gregorius)
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