Trigonal Pyramidal?

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Kelly Cai 4D
Posts: 55
Joined: Sat Jul 20, 2019 12:17 am

Trigonal Pyramidal?

Postby Kelly Cai 4D » Sun Nov 17, 2019 2:20 pm

In lecture, we discussed that this sulfate ion, so3 (2-), has the molecular shape of trigonal planar. However, our textbook states that it's actually trigonal pyramidal. From my understanding, it has 4 regions of electron density and therefore it has an electron arrangement of tetrahedral. However, I was confused what is the actual name of this ion's shape.

Siya Shah 1J
Posts: 50
Joined: Sat Aug 17, 2019 12:15 am

Re: Trigonal Pyramidal?

Postby Siya Shah 1J » Sun Nov 17, 2019 2:23 pm

I believe if the molecule has four regions of electron density, then it cannot be trigonal planar. If it has four regions of electron density, three of which are bonded pairs, then the molecule would be called trigonal pyramidal.

Lauren Sanchez 3D
Posts: 52
Joined: Sat Aug 24, 2019 12:17 am

Re: Trigonal Pyramidal?

Postby Lauren Sanchez 3D » Sun Nov 17, 2019 2:33 pm

In this compound, is it trigonal pyramidal because even though there are 4 regions of e- density, one of the regions is a lone pair?

Sydney Pell 2E
Posts: 80
Joined: Wed Sep 11, 2019 12:17 am

Re: Trigonal Pyramidal?

Postby Sydney Pell 2E » Sun Nov 17, 2019 2:52 pm

A trigonal planar molecule must have no more than three areas of electron density, and all three must be bonding pairs. SO3 (2-) has three bonding pairs, but since it also has a lone pair, it would then be trigonal pyramidal since the lone pair would repulse the bonding pairs away from it.

Sydney Pell 2E
Posts: 80
Joined: Wed Sep 11, 2019 12:17 am

Re: Trigonal Pyramidal?

Postby Sydney Pell 2E » Sun Nov 17, 2019 2:57 pm

There are four regions of electron density, which means the electron geometry is tetrahedral. Since one is a lone pair, the molecular geometry is trigonal pyramidal.


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