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Trigonal Pyramidal?

Posted: Sun Nov 17, 2019 2:20 pm
by Kelly Cai 4D
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.

Re: Trigonal Pyramidal?

Posted: Sun Nov 17, 2019 2:23 pm
by Siya Shah 1J
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.

Re: Trigonal Pyramidal?

Posted: Sun Nov 17, 2019 2:33 pm
by Lauren Sanchez 3D
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?

Re: Trigonal Pyramidal?

Posted: Sun Nov 17, 2019 2:52 pm
by Sydney Pell 2E
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.

Re: Trigonal Pyramidal?

Posted: Sun Nov 17, 2019 2:57 pm
by Sydney Pell 2E
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.