Lone Pairs

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

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Sunjum Singh 1I
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Joined: Fri Apr 06, 2018 11:05 am

Lone Pairs

Postby Sunjum Singh 1I » Sat Jun 02, 2018 3:20 pm

So when determining the molecular shape, lone pairs are considered a region of electron density but they don't make it the shape associated with that number of e- density regions correct? For example NH3 has 4 regions of electron density, one of which being a lone pair, but that doesn't make the shape tetrahedral but trigonal pyramidal?

Marisol Sanchez - 1E
Posts: 38
Joined: Fri Apr 06, 2018 11:05 am

Re: Lone Pairs

Postby Marisol Sanchez - 1E » Sat Jun 02, 2018 3:36 pm

That is exactly correct. The lone pairs influence the overall shape and account for a region of electron density but not directly so that four regions, including one lone pair, would not yield tetrahedral. This only occurs with 4 bonds.

nicolesalcedo
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am

Re: Lone Pairs

Postby nicolesalcedo » Sat Jun 02, 2018 4:27 pm

To add on, the lone pairs will push away from the bonds stronger, making bond angles smaller. Thus, looking at the VSEPR formula is extremely helpful when determining shape. For example, AX3 will yield trigonal planar with bond angles 109.5 but AX3E will yield trigonal pyramidal with bond angles <109.5. The lone pair pushed the bonds closer together.


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