Why is water MG Bent?!

[fgari]

So if Molecular Geometry does not consider lone pairs then why is water MG Bent?

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[ll REVOFEV ll]

So if Molecular Geometry does not consider lone pairs then why is water MG Bent?

I thought molecular geometry considers lone pairs....which is why water MG would be bent..maybe I'm mistaken.

 

[fgari]

I thought molecular geometry considers lone pairs....which is why water MG would be bent..maybe I'm mistaken.

Chad says they do not. I've been going through his videos while on the 8 week plan and can't figure it out.

 

[fellforit]

Okay, I haven't gotten to this part of Chad's yet, but as far as I can tell:

Molecular geometry doesn't consider lone pairs in the sense that if you have a lone pair you don't count it when talking about geometry. So, if you have a lone pair and then three substituents, your geometry is trigonal pyramidal, not tetrahedral, because you don't count the lone pair as a substituent. BUT that lone pair is still affecting the geometry, which is why the molecule is trigonal pyramidal and not trigonal planar -- because that lone pair is pushing the other molecules away.

Hope that helps...

 

[Immutef]

Okay, I haven't gotten to this part of Chad's yet, but as far as I can tell:

Molecular geometry doesn't consider lone pairs in the sense that if you have a lone pair you don't count it when talking about geometry. So, if you have a lone pair and then three substituents, your geometry is trigonal pyramidal, not tetrahedral, because you don't count the lone pair as a substituent. BUT that lone pair is still affecting the geometry, which is why the molecule is trigonal pyramidal and not trigonal planar -- because that lone pair is pushing the other molecules away.

Hope that helps...

👍

OP, if you need more clarification, google electron pair geometry vs. molecular geometry.



Water has a tetrahedral electron pair geometry, but a bent molecular geometry.

*post edited to add picture

 

[Parle G]

I think MG does take into account lone pairs. The way I solve these problems is that I look at how many electron domains are around the molecule. For example, in H2O there are 4 electron domains (2 which are bonds, and two lone pairs); If you look at Chad's outline, you will see that a chemical structure with 4 electron domains and two lone pairs has a molecular geometry that is bent.

On a side note, if there were no lone pairs, then MG will be equal to the electron domain geometry. So in CH4, for instance, there are 4 electron domains, and no lone pairs; so, the electron domain geometry will be the same as molecular geometry (tetrahedral).

 

[shootingstar7]

So if Molecular Geometry does not consider lone pairs then why is water MG Bent?

You don't count the lone pairs as substituents. If you did, then you would consider the molecule a tetrahedral one.
But, they DO affect the geometry, due to the electron pairs repelling the two substiuents. The electrons force the hydrogens away, "bending" the form, so instead of being linear, the molecule is bent.

 

[invictusx]

So if Molecular Geometry does not consider lone pairs then why is water MG Bent?

Water is absolutely bent. Consider molecular orbitals and electron repulsions. Forget general chemistry, think organic chemistry.

 

[fgari]

Awesome! thanks for the replies everyone!! All cleared up now 😀