molecular shape

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

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Katherine Chhen 3I
Posts: 53
Joined: Fri Sep 28, 2018 12:15 am

molecular shape

Postby Katherine Chhen 3I » Wed Nov 13, 2019 1:44 pm

Based on the lewis structure, how are we able to determine the molecular shape since the lewis structure is only 2-D?

Lindsey Chheng 1E
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

Re: molecular shape

Postby Lindsey Chheng 1E » Wed Nov 13, 2019 1:47 pm

Katherine Chhen 3I wrote:Based on the lewis structure, how are we able to determine the molecular shape since the lewis structure is only 2-D?

To determine molecular shape, you have to take into account the steric number (# bonding regions + lone pairs) and the number of lone pairs. Determining the name of the molecular shape will basically depend on memorization skills.

Shutong Hou_1F
Posts: 117
Joined: Sat Sep 14, 2019 12:17 am

Re: molecular shape

Postby Shutong Hou_1F » Wed Nov 13, 2019 3:24 pm

There are several general rules to help determine, and thus memorization is required.
To determine the molecular shape, both lone pair electrons and bonding pair electrons need to be considered; professor Lavelle hasn't discussed this in lecture yet.
However, to name the shape of the molecule, only positions of bond atoms, or bonding electron pairs need to be considered.
To name the molecular shape:
1) linear, 2 bonding pairs;
2) trigonal planar, 3 bonding pairs;
3) tetrahedral, 4 bonding pairs;
4) trigonal bipyramidal, 5 bonding pairs;
5) octahedral, 6 bonding pairs;

simmoneokamoto3K
Posts: 50
Joined: Mon Jun 17, 2019 7:22 am

Re: molecular shape

Postby simmoneokamoto3K » Wed Nov 13, 2019 3:33 pm

Shutong Hou_3I wrote:There are several general rules to help determine, and thus memorization is required.
To determine the molecular shape, both lone pair electrons and bonding pair electrons need to be considered; professor Lavelle hasn't discussed this in lecture yet.
However, to name the shape of the molecule, only positions of bond atoms, or bonding electron pairs need to be considered.
To name the molecular shape:
1) linear, 2 bonding pairs;
2) trigonal planar, 3 bonding pairs;
3) tetrahedral, 4 bonding pairs;
4) trigonal bipyramidal, 5 bonding pairs;
5) octahedral, 6 bonding pairs;


As the person mentioned above, how its taught is that we should draw the lewis structure of the molecule initially (this includes meaning finding the resonance if necessary) and then seeing the configuration and as there are only five configurations, it should be fairly easy

Ariel Davydov 1C
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Joined: Thu Jul 11, 2019 12:16 am
Been upvoted: 1 time

Re: molecular shape

Postby Ariel Davydov 1C » Wed Nov 13, 2019 3:36 pm

There are also some really great Youtube videos that help you visualize the shapes of these molecules and understand them rather than depending on sole memorization. I highly recommend Tyler DeWitt's video on VSEPR. Hope this helps!

Victoria Otuya 4F
Posts: 50
Joined: Wed Sep 18, 2019 12:21 am

Re: molecular shape

Postby Victoria Otuya 4F » Wed Nov 13, 2019 7:53 pm

So first drawing the lewis structure can help, next is counting the bonds and lone pairs on the central atom, and then assigning the electron arrangement and lastly is identifying the shape considering only atoms.

Katherine Chhen 3I
Posts: 53
Joined: Fri Sep 28, 2018 12:15 am

Re: molecular shape

Postby Katherine Chhen 3I » Thu Nov 28, 2019 9:59 am

Would we need to draw the Lewis structure with the correct formal charge in order to determine the molecular shape? Or can we just draw a general Lewis structure?

kim 2I
Posts: 105
Joined: Thu Jul 25, 2019 12:17 am

Re: molecular shape

Postby kim 2I » Thu Nov 28, 2019 3:21 pm

You should still draw the Lewis structure with the lowest formal charges since the number of bonds/lone pairs could change and therefore affect the molecular shape. However, you don't need to worry about resonance structures.

Catherine Daye 1L
Posts: 104
Joined: Wed Sep 11, 2019 12:16 am

Re: molecular shape

Postby Catherine Daye 1L » Thu Nov 28, 2019 3:33 pm

You look at the regions of electron density. Count the number of bonds and lone electron pairs around the central atom. That shows you the VSEPR formula (AXE), and you can determine the molecular shape.


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