## tetrahedral vs trigonal planar

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

katietietsworth_3c
Posts: 31
Joined: Fri Sep 28, 2018 12:24 am

### tetrahedral vs trigonal planar

I am having trouble distinguishing between tetrahedral and trigonal planar, how can I know which the Lewis structure is?

Samantha Kwock 1D
Posts: 61
Joined: Fri Sep 28, 2018 12:24 am

### Re: tetrahedral vs trigonal planar

Tetrahedral geometry requires four atoms bonded to a central atom. Trigonal planar only has three atoms bonded to the central atom.

emily gao 1C
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

### Re: tetrahedral vs trigonal planar

tetrahedral has 4 bonding regions, while trigonal planar has only 3. When you look at the lewis structure of the central atom, look at how many bonding regions it has.

michelle
Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

### Re: tetrahedral vs trigonal planar

You can simply distinguish them with the number of atoms as the above posts say, or imagine the shape based on Lewis structures. Pay attention to lone pairs.

Desiree1G
Posts: 62
Joined: Fri Sep 28, 2018 12:16 am
Been upvoted: 2 times

### Re: tetrahedral vs trigonal planar

So what helps best is to draw the Lewis structure of the compound. So you have your central atom and typically the other surrounding atoms. If there are no lone pairs and it has 4 surrounding atoms it is tetrahedral (tetra=4). However, if it is trigonal planar (tri=3) then it only has 3 surrounding atoms. Keep in mind lone pairs change the shape because of electron repulsion.

Danny Elias Dis 1E
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: tetrahedral vs trigonal planar

How many lone pairs are possible when the molecule is in the trigonal planar shape?

KHuang1L
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: tetrahedral vs trigonal planar

Tetrahedral means that there are four atoms bound around a central atom. Trigonal planar is when there are three atoms bound around a central atom. You can memorize the A, X, and E for each structure to better identify them in the future.

Kelly Hollman
Posts: 33
Joined: Fri Sep 28, 2018 12:27 am

### Re: tetrahedral vs trigonal planar

Danny Elias Dis 1E wrote:How many lone pairs are possible when the molecule is in the trigonal planar shape?

There can be 3 regions for this shape, but I think we've only seen molecules in this shape with one lone pair, e.g. SO2, a bent shape.

Lynsea_Southwick_2K
Posts: 55
Joined: Fri Sep 28, 2018 12:25 am

### Re: tetrahedral vs trigonal planar

What helps me is looking at the VSEPR formula. They are distinct from one another.

Chloe Thorpe 1J
Posts: 77
Joined: Fri Sep 28, 2018 12:16 am

### Re: tetrahedral vs trigonal planar

It helps me to just remember that tetrahedral has a general formula of AX4 while trigonal planar has a formula of AX3. (A being the central atom and X being bound atoms)