Lone Pairs

(Polar molecules, Non-polar molecules, etc.)

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salvadorramos3k
Posts: 72
Joined: Wed Sep 18, 2019 12:18 am

Lone Pairs

Postby salvadorramos3k » Sat Nov 16, 2019 6:55 pm

How is it that sometimes a molecule has 4 bonding regions (one of them being a lone pair) but the shape is not tetrahedral? In class my TA was showing up examples of identifying shapes and he would erase the lone pair, but I'm not sure why. Do lone pairs not really matter, just the actual bonds?

Anish Patel 4B
Posts: 59
Joined: Thu Jul 11, 2019 12:17 am

Re: Lone Pairs

Postby Anish Patel 4B » Sat Nov 16, 2019 6:58 pm

lone pairs count towards molecular geometry not electron domain geometry. so in the case of 4 electron domains (3 bonding and one lone pair), the electron domain geometry would be tetrahedral while the molecular geometry would be trigonal pyramidal.

charleejohnson1L
Posts: 99
Joined: Fri Aug 30, 2019 12:17 am

Re: Lone Pairs

Postby charleejohnson1L » Sat Nov 16, 2019 7:53 pm

The geometry is based purely on electron dense areas, but the VSEPR model only uses the bonded parts, as the repulsion will cause all electron-dense areas to move as far away from each other. :) I hope this helps.

Kayla Maldonado 1C
Posts: 107
Joined: Sat Aug 17, 2019 12:16 am
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Re: Lone Pairs

Postby Kayla Maldonado 1C » Sun Nov 17, 2019 12:38 am

Anish Patel 4B wrote:lone pairs count towards molecular geometry not electron domain geometry. so in the case of 4 electron domains (3 bonding and one lone pair), the electron domain geometry would be tetrahedral while the molecular geometry would be trigonal pyramidal.

So if asked in a question what shape a certain molecule would have, would we give the electron domain geometry or molecular geometry, in your example tetrahedral or trigonal pyramidal?

Emily_4B
Posts: 57
Joined: Wed Sep 18, 2019 12:21 am

Re: Lone Pairs

Postby Emily_4B » Sun Nov 17, 2019 12:42 am

Kayla Maldonado 1A wrote:
Anish Patel 4B wrote:lone pairs count towards molecular geometry not electron domain geometry. so in the case of 4 electron domains (3 bonding and one lone pair), the electron domain geometry would be tetrahedral while the molecular geometry would be trigonal pyramidal.

So if asked in a question what shape a certain molecule would have, would we give the electron domain geometry or molecular geometry, in your example tetrahedral or trigonal pyramidal?

I believe you would say the shape is a trigonal pyrimidal

Ashley R 1A
Posts: 41
Joined: Sat Aug 24, 2019 12:16 am

Re: Lone Pairs

Postby Ashley R 1A » Sun Nov 17, 2019 1:11 am

This concept also applies to 5 electron densities.

For 5 electron densities where all 5 are bonds, we have a trigonal bi-pyramidal molecular geometry.
However when we have 4 bonds and 1 unshared electron pair we have a seesaw geometry.

Merin Padayatty 3G
Posts: 52
Joined: Thu Jul 11, 2019 12:16 am

Re: Lone Pairs

Postby Merin Padayatty 3G » Sun Nov 17, 2019 8:32 am

The actual shape of the molecule is dependent on the bonding electron pairs.


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