Linear vs angular and trigonal planar vs trigonal pyramidal

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

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Keshav Bhatnagar 1H
Posts: 32
Joined: Fri Sep 28, 2018 12:17 am

Linear vs angular and trigonal planar vs trigonal pyramidal

Postby Keshav Bhatnagar 1H » Wed Nov 14, 2018 6:30 pm

When you have two electron clouds, how do you figure out if the shape is linear or angular? Same thing with trigonal; If you have 3 electron clouds how do you figure out if the shape is trigonal planar or trigonal pyramidal?

bonnie_schmitz_1F
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Joined: Fri Sep 28, 2018 12:24 am
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Re: Linear vs angular and trigonal planar vs trigonal pyramidal

Postby bonnie_schmitz_1F » Wed Nov 14, 2018 6:49 pm

You need to look at whether the electrons clouds are bonded electrons or lone pair electrons. When determining a molecule's VSEPR structure you look at bonded molecules, but also need to take into account where the lone pair electrons, if there are any, are located. As for your question, below are the classifications for the various molecular shapes:

linear - one central atom, two bonded molecules (2 electron clouds)
angular - one central atom, two bonded molecules, one lone pair electrons (3 electron clouds)
trigonal planar - one central atom, three bonded molecules (3 electron clouds)
trigonal pyramidal - one central atom, three bonded molecules, one lone pair electrons (4 electron clouds)

Matthew Tran 1H
Posts: 165
Joined: Fri Sep 28, 2018 12:16 am

Re: Linear vs angular and trigonal planar vs trigonal pyramidal

Postby Matthew Tran 1H » Wed Nov 14, 2018 7:24 pm

When there are only two regions of electron density, the only logical shape is linear (180 degrees bond angles). Trigonal pyramidal comes from the tetrahedral electronic structure (4 regions of electron density); the only difference is the number of lone pairs. The molecule will be tetrahedral when there are 4 bonding pairs and 0 lone pairs and trigonal pyramidal when there are 3 bonding pairs and 1 lone pair. Remember, there are still 4 regions of electron density (hence the tetrahedral electronic structure), but ignoring the lone pairs when naming the shape gives us trigonal pyramidal.You can get angular from either a tetrahedral electronic structure with 2 lone pairs around the central atom or a trigonal planar electronic structure with one lone pair using the same logic.


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