2E1 - Molecules with bent geometry

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nicolely2F
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2E1 - Molecules with bent geometry

Postby nicolely2F » Thu Nov 14, 2019 10:22 pm

Exercise 2E.1 displays one bent molecule and one linear molecule. The answer key says that the linear molecule "may have" (not necessarily has) lone pairs of electrons on the central atom. I have a theory for why this is possible (since the textbook didn't mention this, at least not in 2E); is it when the central atom has more than 1 lone pair (in addition to e.g. 2 bound atoms) and these lone pairs cancel each other out, allowing for a linear geometry? I'd also appreciate examples!

Qilan Li 4I
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Re: 2E1 - Molecules with bent geometry

Postby Qilan Li 4I » Thu Nov 14, 2019 10:34 pm

I think a good example would be XeF2 where it has 2 bound atoms and 3 lone pairs. Another example would be I3.

chrisleung-2J
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Re: 2E1 - Molecules with bent geometry

Postby chrisleung-2J » Thu Nov 14, 2019 10:36 pm

Yes, although most molecules in which the central atom has lone pairs of electrons have a dipole moment, there are some exceptions in which the dipole moments caused by the lone pairs of electrons cancel out. One example of this is the configuration AX2E3, which is linear due to the three lone pairs of electrons around the central atom having diploe moments which cancel out, thereby resulting in a linear configuration.

Ashley Tran 2I
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Re: 2E1 - Molecules with bent geometry

Postby Ashley Tran 2I » Thu Nov 14, 2019 11:32 pm

For this problem, I found it useful to look at the bond angles. The first example, bent, has angles 120 degrees and we know that for a bent electron arrangement, there must be 2 bonding pairs and 1 or 2 lone pairs. Therefore, in the diagram, when only 2 bonding pairs are shown, we know we must have at least one more lone pair. On the other hand, the second example shows a molecule with a bond angle of 180 degrees. We know this must is a linear molecular shape and therefore there are 2 bonding pairs and 0 lone pairs. However, the electron arrangement with 2 bonding pairs and 3 lone pairs is also linear, therefore, in this example, there may be lone pairs, but it is not required like the first one.

005384106
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Re: 2E1 - Molecules with bent geometry

Postby 005384106 » Fri Nov 15, 2019 9:19 am

Do lone pair electrons have a stronger force of repulsion of atoms compared to the strength of atoms repelling against each other?

Emily Chirila 2E
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Re: 2E1 - Molecules with bent geometry

Postby Emily Chirila 2E » Fri Nov 15, 2019 3:12 pm

005384106 wrote:Do lone pair electrons have a stronger force of repulsion of atoms compared to the strength of atoms repelling against each other?


These are the relative strengths of repulsion:
lone-lone pair repulsion > lone-bonding pair repulsion > bonding-bonding pair repulsion

Julia Mazzucato 4D
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Re: 2E1 - Molecules with bent geometry

Postby Julia Mazzucato 4D » Fri Nov 15, 2019 3:35 pm

Emily Chirila 3D wrote:
005384106 wrote:Do lone pair electrons have a stronger force of repulsion of atoms compared to the strength of atoms repelling against each other?


These are the relative strengths of repulsion:
lone-lone pair repulsion > lone-bonding pair repulsion > bonding-bonding pair repulsion


I've heard from a past student knowledge of this hierarchy is important in a test question at some point, either on the second exam or final.

005384106
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Joined: Sat Aug 24, 2019 12:16 am

Re: 2E1 - Molecules with bent geometry

Postby 005384106 » Mon Nov 18, 2019 5:47 pm

What is the difference between lone-lone pair repulsion, lone-bonding pair repulsion, and bonding- bonding pair repulsion? I thought there was only repulsion differences of 2 types such as a lone pair electron pair and an atom.


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