Lone pairs determining shape?

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

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Lone pairs determining shape?

Postby juleschang16 » Sat Nov 24, 2018 3:52 pm

In the textbook, it says that lone pairs are not included when identifying molecular shapes. However, I thought we learned in class that the number of lone pairs and bonds determine the shape of molecules. Can someone clarify which one is correct?

Hanniel U 2B
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Re: Lone pairs determining shape?

Postby Hanniel U 2B » Sat Nov 24, 2018 3:59 pm

Just to be on the safe side, I identify each shape as the parent shape and molecular shape. For example, S02 has a parent shape that is trigonal planar because of its lone pair on S but the molecular shape for S02 is bent or angular.

Madelyn Romberg 1H
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Re: Lone pairs determining shape?

Postby Madelyn Romberg 1H » Sat Nov 24, 2018 4:50 pm

There are two versions of a molecule that we use to identify shape. The molecular shape does NOT use lone pair electrons when determining shape; however, they play an influence in bond angles that can therefore slightly alter the molecular shape. The electronic geometry of a molecule does consider lone pair electrons.

Madeline Motamedi 4I
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Re: Lone pairs determining shape?

Postby Madeline Motamedi 4I » Sat Nov 24, 2018 5:17 pm

So how I interpreted this is that you use your lone pairs to draw the correct shape although once you've classified the shape using the amount of regions of electron density you ignore your lone pairs. Whatever you are left with is what you will use to name the final structure.

Eunice Lee 1A
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Re: Lone pairs determining shape?

Postby Eunice Lee 1A » Sat Nov 24, 2018 11:58 pm

Lone pairs affect bond angles and molecular shape since they also have a charge. However, the molecular shape has to do with the shape of the actual molecule, not the electrons, so they are not accounted for in that sense.

Alan Chang
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Re: Lone pairs determining shape?

Postby Alan Chang » Sun Nov 25, 2018 12:34 am

Lone pairs affect the molecular shape, but only atoms are used when naming the shape. For example, a trigonal pyramidal structure is actually a tetrahedral formation of electron densities, but only the atoms are counted towards the shape, thus the shape is trigonal pyramidal.

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