## Trigonal Shapes

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

harperlacroix1a
Posts: 43
Joined: Fri Sep 28, 2018 12:19 am

### Trigonal Shapes

What is the difference between trigonal planar and trigonal pyramidal? why are the bond angles in trigonal planar 120 degrees but the angles in trigonal pyramidal differ?

Henry Krasner 1C
Posts: 64
Joined: Fri Sep 28, 2018 12:15 am

### Re: Trigonal Shapes

Trigonal planar is 3 bonds, whereas trigonal pyrimidal is 3 bonds and 1 lone pair.

Sabrina Ryu 3L
Posts: 30
Joined: Fri Sep 28, 2018 12:26 am

### Re: Trigonal Shapes

Trigonal planar is flat while trigonal pyramidal is bent! This is because a molecule with trigonal pyramidal shape has a lone pair that repels the other three atoms bonded to the central atom. Trigonal planar molecules have a bond angle of 120 degrees because 360/3 = 120. However, trigonal pyramidal has a shape more like a tetrahedral molecule, which has bond angles of 109.5 degrees. The lone pair on the central atom acts with a stronger repelling force than the fourth bonded atom on a tetrahedral atom, so the bond angles are slightly less than 109.5 degrees.

marinhaluza_1
Posts: 15
Joined: Fri Sep 28, 2018 12:16 am

### Re: Trigonal Shapes

Trigonal Planar only has three areas of electron density whereas trigonal pyramidal has four, one of them being a pair of lone pair electrons. The bond angles for a trigonal planar molecule is 120 because that is as far apart from each other as possible and trigonal pyramidal is a little less than 109.5 because the lone pair of electrons is very repulsive and therefore push the bonds a little closer together. Hope this helped(:

Aurbal Popal
Posts: 63
Joined: Fri Sep 28, 2018 12:27 am

### Re: Trigonal Shapes

Like Henry said, trigonal planar has three bonds and hence three electron densities. All the electron densities are on one plane and are 120 degrees apart from each other as that is the farthest apart they can be from each other.
Trigonal pyramidal also has three bonds, but they also have one lone pair. This means they have four electron densities. However, it is not a tetrahedral since the lone pairs are very repulsive, so the three bonds are pushed away from it, causing them to have a smaller bond angle. They are also found in more than one plane.