How to remember molecule shapes using vsepr theory easily

Dear student

 

I personally found this "order" of memorizing it to be easiest.

1. First off I find it simple to memorize the structures in groups according to steric number/ Bonding number.

Steric number 2 = 1 structure

Steric number 3 = 2structures

Steric number 4 = 3 structures

Steric number 5 = 4 structures

Steric number 6 = 3 structures.

Last one kind of breaks the rule but I still find this helps.

 

2. Now you have to memorize the structures in each steric number group.

 

Steric number 2 = Linear (180 degrees)

Steric number 3 = Bent and Trigonal Planar (Both 120 degrees)

Steric number 4 = Tetrahedral, Trigonal Bipyramidal and Bent again. (109.5, 107.3 and 104.5 degrees)

Steric number 5 = Trigonal Bipyramidal, See-Saw, T-Shaped and Linear (Mixture of 90, 120 and 180 degrees)

Steric number 6 = Square Planar, Square Pyramid and Octahedral (All 90 degrees)

 

3. Now this seems like a lot but, for me personally, I try to find a relation between all the groups.

 

For groups 2 and 3, I just kind of remember that they're those shapes it's pretty straightforward I think.

 

Group 4 are all tetrahedral shaped molecules (Think group "4" / "Tetrahedral") with slight variations on the bond angles based on the amount of lone pairs. Tetrahedral is the most uniform shape and it has a bond angle closest to 120, with a slight repulsion from the uppermost atom making a bond angle of 109.5. Trigonal Bipyramidal has a lone pair of electrons which pushes the "side atoms" a little further away from 120 forming an angle of 107.3. Lastly, this variation of bent has two lone pairs of electrons pushing the "side atoms" even further away making an angle of 104.5.

 

Group 5, to me, are the "wierd shapes". This includes the trigonal bipyramidal, see-saw, T-shape and linear. I don't have much for this one. T shape is 90 degrees because in the letter T, only 90 degree angles are present. Linear is obviously 180 degrees. See-saw has 3 angles and i remember them by picturing an actual see-saw in my head with 1 angle along the top of the seat (180), 1 between the seats and the legs (90), and one between the two legs (120). and trigonal Bipyramidal has 2 angles, 90 and 120 degrees.

 

Group 6 is the "square group" including: Square planar, square pyramid and octahedral. (I know the last one isnt a square but, close enough). All squares consist of only 90 degree angles so these all only have 90 degree angles.

 

Using ALLLL of this info you can kind of intuitively put together the notation for each structure.

 

This is how I remember them. It might not help everyone else, but basically the only thing you need to take from this if it makes no sense to you is:

 

Memorize the steric numbers, from that you get the amount of structures so you know you're not forgetting any. If you find a way to relate the groups together, it helps memorizing the angles like such since the angles in each steric group are similar.

 

Good luck, I hope this makes sense to other people as much as it makes sense to me and I apologize in advance if this isn't as clear as I mean it to be.