Seesaw Structure question

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FCervania 1B
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Joined: Wed Jun 28, 2017 3:00 am

Seesaw Structure question

Postby FCervania 1B » Sun Jul 16, 2017 1:28 pm

Can someone explain why the seesaw structure of SF4 is preferred instead of placing the lone pair at the "top" of the pyramid?
I understand the goal is to get less repulsion, but how does placing the lone pair in the "middle" of a seesaw creates less repulsion rather than at the top of the triagonal pyramid.

Also, when drawing the lewis structure for SF4, is it necessary to draw it similar to the letter "K" (refer to top of page 99 in course reader) or can we draw it as an actual seesaw, if that is how we remember it conceptually,

Thank you

Davalanya 1F
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Joined: Fri Jun 23, 2017 11:39 am
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Re: Seesaw Structure question

Postby Davalanya 1F » Sun Jul 16, 2017 3:56 pm

What I understand about the VSEPR model is that it always you to take into consideration the lone pairs. Lone pairs on the Lewis structure cause the shape to change. It's not a simple move as placing the electron on top, the structures take into account the repulsion and polarity of the molecule. I don't necessarily understand what you mean by drawing a seesaw in the literal sense and when it's a K shape, but if you draw a see-saw draw it up right?

Jordan Larrea 1E
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Joined: Fri Jun 23, 2017 11:39 am

Re: Seesaw Structure question

Postby Jordan Larrea 1E » Sun Jul 16, 2017 10:14 pm

In the seesaw, you have 4 atoms and an electron pair. The pair does repel a good amount, but the repulsion of the other atoms cannot be neglected. To put the electrons on top and have the other 4 as a pyramid base would have too much repulsion from the 4 atoms. the seesaw shape puts enough space between everything.

In terms of drawing it, the orientation shouldn't matter so much. Whether you draw it as a "k" or a seesaw, just make sure you use the correct filled in triangle and triangle made of lines (don't know what to call it). The professor said we won't be doing so much drawing. We'll mostly just have to name the shapes.

JD Malana
Posts: 21
Joined: Wed Nov 16, 2016 3:02 am

Re: Seesaw Structure question

Postby JD Malana » Sun Jul 16, 2017 11:24 pm

So basically we should check if any other arrangement would put more space between the electrons than the one we come up with? And if there are none then it's good?

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