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### Determining Shape

Posted: Sat Nov 17, 2018 11:04 pm
I was wondering if there was an easy short way in determining the shape of a molecule based on its molecular formula without drawing the Lewis structure first? Or is the Lewis structure necessary for determining the shape?

### Re: Determining Shape

Posted: Sat Nov 17, 2018 11:22 pm
you want to draw out the lewis structure always to determine what the Steric Number is for the central atom...then you can determine shape from there.

oh and steric number means bonded pairs of electrons (double bond counts as one) AND lone pairs of electrons

have a good thanksgiving :)

### Re: Determining Shape

Posted: Sat Nov 17, 2018 11:25 pm
you want to draw out the lewis structure always to determine what the Steric Number is for the central atom...then you can determine shape from there.

oh and steric number means bonded pairs of electrons (double bond counts as one) AND lone pairs of electrons

have a good thanksgiving :)

### Re: Determining Shape

Posted: Sat Nov 17, 2018 11:54 pm
You will always need to draw the lewis structure because a compound can have numerous structures drawn and you need to find the one with the lowest energy to be able to find the correct shape as well as the reason mentioned above.

### Re: Determining Shape

Posted: Sun Nov 18, 2018 11:12 am
I think its best to always draw the lewis structure so you can get the most accurate answer. This way you will be able to find the shape, lone pairs, etc..

### Re: Determining Shape

Posted: Sun Nov 18, 2018 12:08 pm
It is hard to know the number of bonding pairs and lone pairs just by looking at the chemical formula. I think to be safe we have to draw the lewis structure.

### Re: Determining Shape

Posted: Sun Nov 18, 2018 1:33 pm
I think besides just drawing the Lewis structure, what would also help is sketching or imagining the Lewis structure in 3d. The Lewis structure presents you with a very 2d linear version of what the model actually looks like.

### Re: Determining Shape

Posted: Sun Nov 18, 2018 4:19 pm
It's good to get in the habit of drawing the lewis structure and as you do them more and more it'll be easier and you'll become faster at drawing them.

### Re: Determining Shape

Posted: Sun Nov 18, 2018 4:27 pm
My TA said we can either memorize every shape, or use your intuition. She also said to draw them out.

### Re: Determining Shape

Posted: Sun Nov 18, 2018 4:38 pm
For now I would really just draw the Lewis Structures every time- eventually you may begin to pick up on certain patterns but as of right now drawing the Lewis Structure first is the best way to go!

### Re: Determining Shape

Posted: Sun Nov 18, 2018 7:04 pm
In order to determine molecular shape, you should be able to find the steric number, which is the number of atoms and lone pairs bonded to the central atom.