Silicon Halides vs. Carbon Halides

Jan 2013
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Silicon halides have stronger bonds than corresponding carbon halides. Which is a possible explanation of this phenomenon?

A. Silicon has the ability to form a partial double bond with a halogen through the overlap of its d-orbitals with a p-orbital of the halogens.

B. The larger silicon atoms permit better overlap of its atomic orbitals with those of the halogens than the smaller carbon atoms do.

C. The larger electronegativity difference between silicdon and the halogens make their bonds stronger that those of carbon.

D. Silicon has a larger effective nuclear charge than the carbon which allows it to bond more strongly to the more negative halogens than carbon.

E. Carbon-halogen bonds are usually weak.

I have eliminated C. Please help me answer this question.
 

Unknown008

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A. Do halogen atoms form partial double bonds?
B. Does the extent of overlap affect bond strength?
D. How does the difference in electronegativity affect the bond strength?
E. Why are they usually weak?
 
Jan 2013
18
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A) No
B) Yes
D) The more electronegative the stronger the bond.
E) They are usually weak because they are linked by weak covalent bonding.
 

Unknown008

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A. Good

B. C-C bonds are stronger than Si-Si bonds :) And C atoms are smaller than Si atoms. Remember that diamond is one of the hardest materials on earth?

Oops, that was meant for C :eek:
C. Right, so if you have a big positive atom (mind the term, I'm not speaking about ions!) and a big negative ion, the two attract each other more and the bond is stronger. Atoms at the top right of the periodic table are more electronegative. Atoms at the bottom left of the periodic table are more electropositive. C is above Si, so, C is more negative than Si.

Which means, let's give C a small charge of +1. Si would be something like +2. Let's say halogens have a charge of -1.

Is C bonded to halogen (+1 and -1) stronger than Si bonded to halogen (+2 and -1)?

D. I actually meant to ask instead, how is the effective nuclear charge calculated. Well, nevermind now, the effective nuclear charge is calculated by dividing the charge of the ion by it's size (atomic radius). Since the nuclear charge of C and that of Si are the same, only the size affect the effective nuclear charge. Since now Si is larger than C, C has the higher nuclear charge and Si the lower nuclear charge.

Does it make sense?

E. Actually, there are two main types of covalent bonding: the first is intramolecular bonding and the second is intermolecular bonding.

Intramolecular bonding is the covalent bond within a molecule. Examples are the C-C bond in diamond, the O=O bond in oxygen gas.

Intermolecular bonding is the covalent bond between molecules. Examples are the hydrogen bonding between H2O molecules (the bond which links one molecule to another), or the Van der Waals forces of attraction between two oxygen molecules (the bond which links one O2 to another O2).

The carbon-halogen bond is an intramolecular bond. PVC is a compound which has a C-Cl bond, and I'm sure you've heard about how PVC is great because it is corrosion resistant. This statement in itself is not completely true, and definitely does not explain why silicon halide bonds are stronger than carbon halide bonds.
 
Jan 2013
18
0
Than you for the explanations. :) Based off of the validity of the answer choices, and our discussions, I have chose B for my answer. Is that correct? Or am I missing a key point somewhere.
 

Unknown008

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B. is false. The overlap has nothing to do with the bond strength. For instance, C-C bond is stronger than Si-Si bond, and C-C bond has less overlap than Si-Si bonds.

Try again :)
 

Unknown008

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Hmm, I didn't know that halogens could do partial double bonds. I don't know of any possible =/

Also, if you try a search on that matter, you will find that there are numerous mentions of Carbon - Halide partial double bond as well (I knew that the bond between chlorine and benzene in chloro benzene could be considered like a double bond, but as to acknowledge it was a partial double bond is unheard of me).

Well, for me, the answer would be C, because the larger difference in electronegativity causes a greater force of attraction.