Test 2

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

Moderators: Chem_Mod, Chem_Admin

Areli C 1L
Posts: 95
Joined: Wed Nov 14, 2018 12:19 am

Test 2

Postby Areli C 1L » Thu Nov 21, 2019 3:29 pm

Can someone provide some important concepts to keep in mind for test 2? I have the memory of a goldfish and I really want to do well on this test. Thank you!

Kristina Rizo 2K
Posts: 105
Joined: Wed Sep 18, 2019 12:19 am

Re: Test 2

Postby Kristina Rizo 2K » Thu Nov 21, 2019 3:31 pm

I know the bonds (sigma and pi), molecular shapes, bond angles and the intermolecular forces will be on test 2. I'm not sure if that is all though.

LBacker_2E
Posts: 104
Joined: Wed Sep 18, 2019 12:21 am
Been upvoted: 1 time

Re: Test 2

Postby LBacker_2E » Thu Nov 21, 2019 3:39 pm

I think you are also supposed to know the VSEPR Model, dipole moments and how that is related to polarity, the strength of different intermolecular forces. Anything that is on Homework 3F and 2E may be on the test.

Areli C 1L
Posts: 95
Joined: Wed Nov 14, 2018 12:19 am

Re: Test 2

Postby Areli C 1L » Thu Nov 21, 2019 4:20 pm

Kristina Rizo 3K wrote:I know the bonds (sigma and pi), molecular shapes, bond angles and the intermolecular forces will be on test 2. I'm not sure if that is all though.

Do you know if we will be expected to memorize the bond angles?
I thought he mentioned in lecture that we weren't but maybe I didn't listen correctly.

Cassandra_1K
Posts: 49
Joined: Wed Sep 18, 2019 12:16 am

Re: Test 2

Postby Cassandra_1K » Thu Nov 21, 2019 6:26 pm

Does anyone have any advice for remembering molecular shape?

Rebecca Remple 1C
Posts: 137
Joined: Wed Sep 18, 2019 12:16 am
Been upvoted: 1 time

Re: Test 2

Postby Rebecca Remple 1C » Thu Nov 21, 2019 6:50 pm

Cassandra_1K wrote:Does anyone have any advice for remembering molecular shape?

Hi Cassandra,

I think it's good to start by remembering molecular geometry, where lone pairs are counted as regions of electron density. If there are 2 areas of electron density, the shape is linear and the angle 180 degrees. If there are three areas of electron density, the shape is trigonal planar and has 120 degree angles. If there are four, it is tetrahedral and has 109.5 degree angles. Five is trigonal bipyramidal, which has a mix of 120 and 90 degree angles. Finally, six is octahedral, which has 90 degree bond angles.
After you memorize these main forms, you can consider molecular shape. For this, lone pairs are not counted as regions of electron density, but they still influence shape. There're quite a lot, so I'll only provide a few examples. A molecule with configuration AX2E would be bent and have an angle close to 120 (slightly less because of the repulsion of lone pairs). A molecule with configuration AX4E would be see-saw shaped and have angles around 90 and 120 degrees. I've attached a chart that's been very useful to me, which contains visual representations and bond angles for all molecular shapes. I hope this helps!

-Rebecca
Attachments
molecular geometry and shape.png

Michelle N - 2C
Posts: 117
Joined: Wed Sep 18, 2019 12:19 am

Re: Test 2

Postby Michelle N - 2C » Thu Nov 21, 2019 8:23 pm

Definitely know intermolecular forces (dipole moments) and the concept and shapes from the VSEPR model. Good luck! :)

Jocelyn Thorp 1A
Posts: 103
Joined: Wed Sep 18, 2019 12:20 am

Re: Test 2

Postby Jocelyn Thorp 1A » Fri Nov 22, 2019 2:00 am

Rebecca Remple 1J wrote:
Cassandra_1K wrote:Does anyone have any advice for remembering molecular shape?

Hi Cassandra,

I think it's good to start by remembering molecular geometry, where lone pairs are counted as regions of electron density. If there are 2 areas of electron density, the shape is linear and the angle 180 degrees. If there are three areas of electron density, the shape is trigonal planar and has 120 degree angles. If there are four, it is tetrahedral and has 109.5 degree angles. Five is trigonal bipyramidal, which has a mix of 120 and 90 degree angles. Finally, six is octahedral, which has 90 degree bond angles.
After you memorize these main forms, you can consider molecular shape. For this, lone pairs are not counted as regions of electron density, but they still influence shape. There're quite a lot, so I'll only provide a few examples. A molecule with configuration AX2E would be bent and have an angle close to 120 (slightly less because of the repulsion of lone pairs). A molecule with configuration AX4E would be see-saw shaped and have angles around 90 and 120 degrees. I've attached a chart that's been very useful to me, which contains visual representations and bond angles for all molecular shapes. I hope this helps!

-Rebecca


thank you so much for this chart

andrewcj 2C
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

Re: Test 2

Postby andrewcj 2C » Fri Nov 22, 2019 2:22 am

knowing bond angles of vsepr structures and how lone pairs can affect those bond angles is probably a good idea

Anthony Hatashita 4H
Posts: 103
Joined: Wed Sep 18, 2019 12:21 am

Re: Test 2

Postby Anthony Hatashita 4H » Fri Nov 22, 2019 3:00 am

Does anyone have any advice about studying intermolecular forces?

Alexis 3F
Posts: 49
Joined: Sat Sep 07, 2019 12:18 am

Re: Test 2

Postby Alexis 3F » Sun Nov 24, 2019 4:35 pm

I just did a bunch of the book problems from that section, and I also watched a youtube on intermolecular forces that had a lot of practice problems in it that I did while following along.

san_2F
Posts: 118
Joined: Sat Jul 20, 2019 12:15 am

Re: Test 2

Postby san_2F » Sun Nov 24, 2019 4:51 pm

In regards to studying intermolecular forces, I would say the best way is to read the chapter in the book about them and then do practice problems.

ShreyaKannan1B
Posts: 51
Joined: Wed Sep 11, 2019 12:15 am

Re: Test 2

Postby ShreyaKannan1B » Sun Nov 24, 2019 8:34 pm

Cassandra_1K wrote:Does anyone have any advice for remembering molecular shape?


I memorized the AX formula that went along with the shape.

Kennedi2J
Posts: 101
Joined: Wed Sep 18, 2019 12:20 am

Re: Test 2

Postby Kennedi2J » Sun Nov 24, 2019 8:42 pm

Will we need to know how to draw/know the shape of a molecule with more than one central atom?

Rosa Munoz 2E
Posts: 105
Joined: Wed Sep 18, 2019 12:21 am

Re: Test 2

Postby Rosa Munoz 2E » Sun Nov 24, 2019 8:46 pm

VSEPR shapes, intermolecular forces+ how they relate to boiling point, sigma and pi bonds...


Return to “Determining Molecular Shape (VSEPR)”

Who is online

Users browsing this forum: No registered users and 5 guests