I've been watching some videos on KhanAcademy around VSEPR concept. When they show exactly how the geometry of a molecule is predicted, they initially look at the main atom, perceiving lone pairs of electrons as an electron cloud. After that they say you have to look at the molecule overall and IGNORE any type of lone pairs, once predicting the geometry. I was wondering what the suggest even is to initially store the lone pairs in mind, and the predict the geometry an additional time, ignoring them? I expect it should have some kind of importance? TIA for answers :)
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What's going on here?
Several civilization, excellent skilled chem human being, have posted excellent replies explaining what is going on. Someone seems to have actually trashed the thcheck out by downvoting them all. That really damages the person that posted the question and desires help.
You are watching: Why can we ignore the disposition of the lone pairs on terminal atoms
All the replies seem great. And as so frequently, they match. People say things in different methods (frequently taking right into account what has currently been said), and reading the repertoire of replies is better than any kind of among them.
It have to be a basic tip in a forum such as this... If you have a problem through a reply, say what it is. That boosts the discussion. Downvoting great replies with no posted reason hurts the group.
If there is a problem, soptimal up!
The reason why we suggest a difference in electron geomeattempt and molecular geometry has to carry out with visualization. Atoms, are actual physical things, that if we shrunk dvery own to their size, we would certainly be able to see them. Electrons but are virtually invisible. So if we look at the form of water, we know that the two electron pairs act as a physical barrier that prevent various other atoms from occupying that area. However before, if we try to 'look' at the water, we wont check out anypoint there and also it appears there is an invisible pressure field in that space. So if though water is tetrahedral (bereason of 4 lived in regions), we deserve to just 'see' 2 of things and they appear to be bent.
OP · 2y
Thanks so much, that entirely makes sense as soon as you explain it favor that!
You perform not entirely overlook them, the form still is what it is bereason of the lone pairs. Eg ammonia isn’t trigonal planar it’s trigonal pyramidal bereason the lone pair pushes the hydrogens dvery own. All you are doing is looking at the form the bonded atoms make.
Due to the fact that the lone pairs determine the form, however are not consisted of in the "molecular geometry".
As others have actually detailed, make a distinction between electron geometry and molecular geometry. A excellent presentation of VSEPR does that.
So without watching the videos, I have actually a couple ideas.
When you talk around geometry, you generally just talk about substituents. Water's oxygen is referred to as bent, not tetrahedral, bereason the lone pairs execute not count as substituents. You must take them into account as soon as drawing/thinking around the molecule, but not in the last geometry.
There's also electronic geometry, and it can be walking you through figuring that out, then making use of the number of substituents that tells you the physical geometry.
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