Molecular Shape vs. Geometry

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

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Rebecca Remple 1C
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Molecular Shape vs. Geometry

Postby Rebecca Remple 1C » Wed Nov 20, 2019 3:38 pm

Hey all,

I hope you're doing well! Can someone please explain the difference between molecular shape and geometry? I am having a difficult time understanding which is which, as the different resources I am using have varied definitions. If possible, can you provide examples for both? Thank you in advance and have a great day!

-Rebecca

TarynD_1I
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Joined: Sat Aug 24, 2019 12:17 am

Re: Molecular Shape vs. Geometry

Postby TarynD_1I » Wed Nov 20, 2019 3:47 pm

From what I understand, the geometry is counting up all the areas of electron density, while the shape involves how the areas of electron density from the lone pairs affects the overall shape of the molecule. For example, H20 would have a tetrahedral geometry (because it would have 4 areas of electron density), but the shape would be bent. In other words, geometry is based on the Lewis Structure and does not consider the lone pairs' effect on the molecule, while shape is a 3-D structure that takes into account the lone pairs.

Kavee Dodampahala 4E
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Re: Molecular Shape vs. Geometry

Postby Kavee Dodampahala 4E » Wed Nov 20, 2019 3:51 pm

The electron pair geometry is based only on how many regions of electron density there are around the atom (whether it is a bonding pair or lone pair is irrelevant). If a molecule has 2 regions of electron density, then the electron density is linear, if there is 3: trigonal planar, 4: tetrahedral, 5: trigonal bipyramidal, 6: octahedral. Molecular shape is more specific and it matters how many bonding pairs and lone pairs there are. For example, the t-shaped and see-saw shapes both fall under the trigonal bipyramidal geometry since they both have 5 total regions of electron density. However, t-shaped is 3 bonding pairs and 2 lone pairs and seesaw is 4 bonding pairs and 1 lone pair.

sarahsalama2E
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Re: Molecular Shape vs. Geometry

Postby sarahsalama2E » Wed Nov 20, 2019 5:00 pm

you can think of molecular geometry as the actual (bonded vs lone pairs) and the electron geometry as the "parent" structure, so if its AX4E2, it would be octahedral, and the molecular geometry would be square planar.

Ariel Davydov 1C
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Re: Molecular Shape vs. Geometry

Postby Ariel Davydov 1C » Wed Nov 20, 2019 5:35 pm

Moleuclar geometry and molecular shape are one and the same. What differs, however, is electron geometry, which takes into account all areas of electron density. Molecular shape/geometry considers electron repulsion between lone pairs and lone pairs and atoms. For example, NH3 will have a molecular geometry of trigonal pyramidal and a tetrahedral electron geometry.

Mitchell Koss 4G
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Re: Molecular Shape vs. Geometry

Postby Mitchell Koss 4G » Thu Nov 21, 2019 2:06 pm

The electron domain shape is needed for bond angles but only the molecular shape is specifically asked for on a test for example.


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