Tips on remembering shapes based on atoms in structure?

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

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Ayesha Aslam-Mir 3C
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Joined: Wed Sep 30, 2020 9:43 pm

Tips on remembering shapes based on atoms in structure?

Postby Ayesha Aslam-Mir 3C » Sun Nov 29, 2020 4:47 pm

I was thinking Quizlet haha but I want to have a better understanding than just going off of memorization; what's a tip to remember the structures and angles of molecules? I find myself referring to a table I printed that shows the atoms around the central atom and their shapes+angles, but I have some trouble building the structue in my mind/on paper and was wondering if anyone has any helpful tips that helped them remember structures.

Sunny Wu 3A
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Re: Tips on remembering shapes based on atoms in structure?

Postby Sunny Wu 3A » Sun Nov 29, 2020 4:52 pm

I think for the structures with no lone pairs (eg tetrahedral trigonal bipyramidal etc) you would just have to memorize the names and structures given how many total atoms there are. For the ones with lone pairs, what I do is envision the shape of the molecule if the lone pair was a bonded atom, then remove that atom in my mind and visualize the resulting shape. Once you can visualize the resulting shape (or draw it out) then you can figure out its name and the bond angles. Sorry that I don't have an easier method but I think the key is just to practice. If anyone else has something easier I'd love to hear it!

Mansi Solanki 3A
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Re: Tips on remembering shapes based on atoms in structure?

Postby Mansi Solanki 3A » Sun Nov 29, 2020 4:56 pm

This is the way that I do it, so I don't know if this is the way that works for everyone but essentially I made sure to memorize the main electron domain geometry structures along with their bond angles. Then, whenever a lone pair is present I know that I can use what I know about the electron domain geometry that it belongs to in order to find out what the molecular shape is. This way you can also tell that the bond angle is slightly less than the bond angle of the main electron domain geometry structure since the lone pair would cause a decrease in the bond angle. I think that it would be good to try to see the way in which the lone pairs are added to the original electron domain geometry as well since this way you can start to familiarize yourself with the shape that it forms.

edward_brodell_2I
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Re: Tips on remembering shapes based on atoms in structure?

Postby edward_brodell_2I » Sun Nov 29, 2020 7:45 pm

I also agree on visualizing the shape. As Dr.Lavelle describes, use the "building blocks" to create your model of what you think the molecule most accurately is. If you have lone pairs, the bond will have to be pushed further away to account for electron repulsions, bonded atoms will have a bonding region between the central and peripheral, once you account for the fact that an atom has a total of 360 degrees around them, this gets distributed among the bonds, and more largely by the lone pair on the central atom. It is also really helpful to familiarze oneself with the geometry by understanding the shape of tetrahedron, octahedron, pyramid, etc b/c sometimes if you know the shape, and its angles are smaller than what the repulsions can handle, then it will help to determine the best shape that accounts for electron repulsions. Also look for trends in lone pairs.


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