Top Posters
Since Sunday
T
3
s
3
o
3
G
3
k
3
C
3
a
3
K
3
f
3
j
3
b
3
c
3
Home Q & A Board Science-Related Homework Help Physics
New Topic  
rkurzyna rkurzyna
wrote...
Go to Answer
Posts: 3
Rep: 0 0
11 years ago
Use VESPR theory to predict the shapes of the following species_

a_ CO2
b_ SiCl4
c_ SO3
d_ SCL2
e_ CO
f_ H2Se


Could you show how you got the answers to each seperately?
Read 655 times
5 Replies
Replies
Answer accepted by topic starter
riotsriots
wrote...
#1
Posts: 23
Rep: 0 0
11 years ago
Sign in or Sign up in seconds to unlock everything for free
1

Related Topics

wrote...
#2
11 years ago
i agree with Bill G on everything---except for C

the structure for SO3 is trigonal planar
it's true that the oxygen has double bond, but there aren't any lone electrons on the sulfur atom, therefore it has to be a trigonal planar since no electrons are pushing the oxygen atoms

to determine the structures you have to study/memorize the structures; generally what determines the shape is the lone electrons that wasn't bonded with the elements, then you can use them to determine how they push the other atoms from the central atom
wrote...
#3
11 years ago
VSEPR theory was never intended to be a predictive tool. It works quite well for most simple molecules but in more complex examples there are lots of exceptions. The correct approach should always be to look up the experimentally determined structure and then to use VSEPR to account for it. A subtle difference.
wrote...
#4
11 years ago
Yeah c should be trigonal planar, Please see this diagram: http://img593.imageshack.us/img593/4859/20121226182131.jpg

The sulphur don't follow the octet rule in this one.
wrote...
#5
11 years ago
I would completely disagree with Mike A when he says, "VSEPR theory was never intended to be a predictive tool."  That is EXACTLY what VSEPR theory is for, to predict the shapes of molecules based on the Repulsion of the Valence Shell Electron Pairs.  What is the purpose of VSEPR theory if not to predict the shapes of molecules?  

Mike A may be confusing this with hybridization.  There is no evidence to suggest that orbitals actually hybridize. It was a nice idea that Pauling developed to try to explain the observed geometries of some molecules.  Recently, some chemical educators have suggested that it may be time to retire hybridization.

To use VSEPR theory you should begin with a Lewis structure.  VSEPR theory says....
2 bonding pairs, no lone pairs = linear.  Such is the case for CO2.  The pi bond portion of the double bonds do not establish the geometry, only the sigma-bond portion of the double bond does that.

4 bonding pairs, no lone pairs = tetrahedral.  Such is the case for SiCl4.

Three bonding pairs, no lone pairs = trigonal planar.  Such is the case for SO3.  Danny suggested that there is one double bond, but a better representation of SO3 is THREE double bonds.  The one double bond structure requires that two more resonance structures be drawn, is what you would have if you followed the octet rule.  (Since it works so seldom, I call it the "octet suggestion.") A better method is to use formal charge.  With only one double bond, the formal charges on two oxygen atoms are -2 and sulfur has a formal charge of +2.  But if you have three double bonds, the formal charge for each atom is zero, which is the preferred value.  

You must also realize that there really isn't one double bond and two single bonds.  All three bonds in SO3 are EXACTLY alike due to delocalized pi-bonding.  If we use the three resonance structures, the bond order is 1.33, but if we use the three double bonds in one structure approach the bond order is 2.  The observed bond order for SO3 is about 1.9.  You can see that the actual bond order is closer to the prediction made from the Lewis structure with three double bonds.

BUT!!!  VSEPR doesn't deal with single vs double bonds.  VSEPR theory merely predicts trigonal planar structure with 120 degree bond angles, and that is what we have whether we use the "octet suggestion" or formal charges.

2 bonding pairs and 2 lone pairs = "bent" at an angle of approximately 109.5 degrees, but expect some distortion due to the additional repulsion from the delocalized lone pairs.  Such is the case for both SCl2 and H2Se

And of course CO is linear since there are onlt two atoms.
New Topic      
Quick Reply
Explore
Post your homework questions and get free online help from our incredible volunteers
  1066 People Browsing
Start New Topic Take the Tour CoursesNew Study Tools Topics Trending Browse by Textbook
Live Chat
Related Images
  
 151
  
 349
  
 1069