Lone Pairs in Molecular Shape

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Brianna Brockman 1F
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Joined: Fri Sep 28, 2018 12:23 am

Lone Pairs in Molecular Shape

Postby Brianna Brockman 1F » Fri Nov 16, 2018 12:33 pm

So I want to make sure I understand this correctly: a lone pair in a molecule acts as though it's an atom when in terms of repelling other atoms and the shape, correct? If no, what are examples of times it doesn't behave like this?

Annalyn Diaz 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

Re: Lone Pairs in Molecular Shape

Postby Annalyn Diaz 1J » Fri Nov 16, 2018 12:53 pm

I believe that for the most part what you are saying is correct but I’ll clarify just in case. Lone pair electrons do repel the other electrons on the substituent atoms, which cause the bond angle to be slightly greater than what’s normally expected; in the same case, as a result, the bond angle between the substituent atoms to be slightly less than what’s expected. Lone pair electrons do count as a bonding region but when naming the shape they don’t count. For example, XeF4 has two pairs of lone electrons and is considered an octahedral (electron pair geometry) but when naming the shape, it’s actually just square planar in terms of molecular geometry.

Nikki Bych 1I
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

Re: Lone Pairs in Molecular Shape

Postby Nikki Bych 1I » Fri Nov 16, 2018 1:53 pm

Lone pairs are areas of electron density, so they do take up space (like an atom does), but they depress the bond angles more than a normal atom; I think of it as lone pairs needing elbow room!

Janelle Magaling 3L
Posts: 11
Joined: Thu Oct 04, 2018 12:16 am

Re: Lone Pairs in Molecular Shape

Postby Janelle Magaling 3L » Fri Nov 16, 2018 2:34 pm

Yes, lone pairs repel other atoms. However they do have different repelling force than other atoms, so the bond angles of the other atoms are smaller than if the lone pair were just another atom.

taryn_baldus2E
Posts: 62
Joined: Fri Sep 28, 2018 12:24 am

Re: Lone Pairs in Molecular Shape

Postby taryn_baldus2E » Fri Nov 16, 2018 2:39 pm

Actually, lone pairs have a higher repulsion strength than an atom and work to repulse the bonded atoms, which is why it is important to consider them when finding the electron dispersion arrangement. After that, you will not draw them in the molecular shape, which accounts for why in these cases the dispersion arrangement and the molecular arrangement appear to be different.


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