Molecular geometry


by Godwin Kessy
Tags: geometry, molecular
Godwin Kessy
Godwin Kessy is online now
#1
Mar25-10, 09:22 AM
P: 91
Hey! How can we compute the molecular geometry for molecules and further use the VSEPR since electrons are continouly in motion, of which i actualy expected to hav temporary geometries ie. Oscilatin once an not a fixed or rigid which shows as if the system is static!
Phys.Org News Partner Chemistry news on Phys.org
Computer program could help solve arson cases
Breakthrough harnesses light for controlled chemical reaction
Large-scale identification and analysis of suppressive drug interactions
chemisttree
chemisttree is offline
#2
Mar25-10, 03:10 PM
Sci Advisor
HW Helper
PF Gold
chemisttree's Avatar
P: 3,725
Fluxional compounds do just as you say. They are in a constant state of change. Most amines are examples of this. More stable compounds are in constant motion as well(above absolute zero) but the motion is motion about a certain geometry. The average structure is the one usually shown since it is difficult to draw a vibrating thingy every time you discuss something.
Godwin Kessy
Godwin Kessy is online now
#3
Mar28-10, 03:58 AM
P: 91
Thanks i now get it! But what do you actually mean by fluxional compounds. gec am interested

also do u min that the geometries we actualy predict cary large probability of occurence? Oh what did you actualy mean that it oscilate round the predicted geometry!

chemisttree
chemisttree is offline
#4
Mar29-10, 02:12 PM
Sci Advisor
HW Helper
PF Gold
chemisttree's Avatar
P: 3,725

Molecular geometry


The latter for most compounds. By fluxional I mean that some compounds interconvert between different 'shapes'. Examples of these are the organometallic compounds such as bis(cyclopentadienyl)mercury (II) that exists both as the bis-monohapto and bis-pentahapto complexes. In the bis-monohapto complex the mercury is sigma bonded once to two carbon atoms... one on each of the two cyclopentadiene groups. In the bis-pentahapto complex, the mercury is bonded to every carbon in both cyclopentadienyl groups. That's about as fluxional as you can get.
DrDu
DrDu is offline
#5
Mar30-10, 04:37 AM
Sci Advisor
P: 3,380
You are right, molecules don't have a shape on a fundamental level. The shape arises as a new concept upon application of the Born-Oppenheimer approximation.
Basically, we are replacing the molecular system of interest by a model system of particles with defined shape which is easier to describe. The error e.g. in energy from this approximation is small on a chemical scale but may be too large on a spectroscopic scale.
Godwin Kessy
Godwin Kessy is online now
#6
Apr1-10, 09:44 AM
P: 91
Hey what does the born approximations say on the molecular expresions
DrDu
DrDu is offline
#7
Apr2-10, 05:43 AM
Sci Advisor
P: 3,380
Just google for "Born Oppenheimer" you should find tons of references. A fascinating but high brow book on the topic is "Chemistry, quantum mechanics, and reductionism : perspectives in theoretical chemistry / Hans Primas".


Register to reply

Related Discussions
Molecular Geometry: NH3 Biology, Chemistry & Other Homework 2
The molecular geometry of ClF3 Chemistry 1
Molecular geometry Biology, Chemistry & Other Homework 1
molecular geometry Biology, Chemistry & Other Homework 2
Help with molecular geometry! Biology, Chemistry & Other Homework 2