Sulfite Ion and its Bond Angle
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Sulfite Ion and its Bond Angle
In class we discussed the sulfite ion SO3 2-. I still don’t understand why the bond angle would be 106 rather than 109.5. Can someone explain?
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Re: Sulfite Ion and its Bond Angle
I think Dr. Lavelle said that for the specific sulfite ion, the bond angle is 106 degrees, however it is less important that you know the specific angle, but rather that you know the bond angle is slightly less than 109.5 degrees. The reason the sulfite ion has a slightly smaller bond angle than 109.5 degrees and not exactly 109.5 degrees is because lone-bonding pair repulsions are greater than bonding-bonding pair repulsions. Therefore, the extra lone pair in the sulfite ion repulses the bonding electrons more than a bonding pair, causing a decrease in bond length. Additionally, 109.5 degrees is based on the tetrahedral shape that has 4 total domains of 4 atoms while the sulfite ion, which is trigonal pyramidal (think of a tetrahedral except with a lone pair instead of one atom) has 4 total domains of 3 atoms and 1 lone pair. The one lone pair, decreases the bond length due to increased repulsion of lone-bonding pairs.
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Re: Sulfite Ion and its Bond Angle
I think it's because instead of four bonding pairs in a tetrahedral, you have three bonding pairs and a lone pair of electrons in a trigonal pyramidal molecule. That lone pair of electrons wants to take up more space, thereby pushing down on the molecule. This causes the bond angle to be less than that of the tetrahedral, which is 109.5, thus resulting in a 106 degree angle.
Also, he mentioned that the VSEPR model can predict distortions qualitatively but not quantitatively, so from the model we know that the bond angle for SO3 2- will be less than 109.5, but the exact angle is obtained through observations.
Hope this helps!
Also, he mentioned that the VSEPR model can predict distortions qualitatively but not quantitatively, so from the model we know that the bond angle for SO3 2- will be less than 109.5, but the exact angle is obtained through observations.
Hope this helps!
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Re: Sulfite Ion and its Bond Angle
The S atom has a lone pair, which creates added repulsion since lone-bonding pair repulsion is greater than bond-bond pair repulsion. This repulsion pushes the bonds further from the lone pair and closer together, thus decreasing the bond angle.
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