MSN Home  |  My MSN  |  Hotmail
Sign in to Windows Live ID Web Search:   
go to MSNGroups 
Free Forum Hosting
 
Important Announcement Important Announcement
The MSN Groups service will close in February 2009. You can move your group to Multiply, MSN’s partner for online groups. Learn More
Chemistry Corner[email protected] 
  
What's New
  
  Welcome Page  
  About This Site  
  Message Boards  
  General  
  Inorganic  
  Organic  
  Pictures  
  Random  
  FOR ALL  
  Handy Symbols  
  Chemistry Humor  
    
  Documents  
  Chemistry Sites I  
  Chemistry Sites II  
  Chemistry Sites III  
  Organic Sites I  
  Organic Sites II  
  Analytical Sites I  
  Analytical Sites II  
  Lesson Plan Sites  
  Online Problems  
  Names & Formulas  
  Naming Exercises  
  Equations I  
  Equations II  
  Eq. Exercises I  
  Eq. Exercises II  
  The Mole I  
  The Mole II  
  Mole Exercises  
  Stoichiometry  
  Stoich. Exercises  
  More Communities  
  School's Out!  
  _________________  
  Site Map  
  
  
  Tools  
 
Inorganic : Another Molecular Orbital Question
Choose another message board
View All Messages
  Prev Message  Next Message       
Reply
 Message 2 of 2 in Discussion 
From: MSN Nickname·Steve·  in response to Message 1Sent: 12/19/2004 8:50 AM
This is a surprisingly involved question!  The structure of the SiO32- ion is not analogous to that of carbonate ion, CO32-, where you have three resonance structures each with one C=O double bond, giving an average bond order of 1 1/3.  Silicon as a rule does not form pi-bonds in this fashion.  In fact, the simple ion SiO32- is unknown, just as molecular "SiO2" (analogous to CO2) is unknown; silicon oxides such as quartz and silicates actually occur in more complex structures in which each silicon has four oxygens bound to it in a tetrahedral geometry.  These tetrahedra link together in chains (as in pyroxene, ((SiO32-)n, "chain silicate"), in rings ((SiO32-)n where n = 3 or 6), in sheets (in micas), and in three-dimensional "framework minerals".

I would first consider the Si-O bonds to be simple single bonds (bond order = 1), but it is known that in some cases there is some double bond character due to silicon 3d-orbital overlap with the oxygen 2p orbital (dp-pp bonding), but this is not the same as a C=O double bond which is a classic pi-bond made from side-to-side overlap of 2p orbitals from each atom (pp-pp bonding).  Thus, in actual silicates, it is probably more accurate to describe the Si-O bonds as single bonds, but acknowledging that there may be a dp-pp contribution.
 

Steve