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Lone Pairs in Molecular Shape

Posted: Fri Nov 16, 2018 12:33 pm
by Brianna Brockman 1F
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?

Re: Lone Pairs in Molecular Shape

Posted: Fri Nov 16, 2018 12:53 pm
by Annalyn Diaz 1J
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.

Re: Lone Pairs in Molecular Shape

Posted: Fri Nov 16, 2018 1:53 pm
by Nikki Bych 1I
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!

Re: Lone Pairs in Molecular Shape

Posted: Fri Nov 16, 2018 2:34 pm
by Janelle Magaling 3L
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.

Re: Lone Pairs in Molecular Shape

Posted: Fri Nov 16, 2018 2:39 pm
by taryn_baldus2E
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.