Mnemonics/Tricks for VESPR

[onedirection]

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I was wondering how you guys keep molecular geometry memorized

I feel like the only logical ones are bent, linear, tetrahedral

I have trouble keeping the other ones straight
Square Planar, Trigonal pyramidal, trigonal planar, T-shaped, octahedral, trigonal bipyramidal, seesaw

and deciding what looks like what

I remember realizing some pattern when I took gen chem like 2 years ago, but I have no idea what is is anymore

It had something to do with decreasing number of electron pairs or something like that and how the changing # of electron pairs influence bond angles, but I can't seem to figure it out anymore

 

[FeinMS]

No, every shape is logical in that it maximizes the distance between substituents or lone pairs to minimize the repulsion. Science is logic

 

[gettheleadout]

No, every shape is logical in that it maximizes the distance between substituents or lone pairs to minimize the repulsion. Science is logic

Quantum mechanics would like a word with you. 😛

 

[mehc012]

I was wondering how you guys keep molecular geometry memorized

I feel like the only logical ones are bent, linear, tetrahedral

I have trouble keeping the other ones straight
Square Planar, Trigonal pyramidal, trigonal planar, T-shaped, octahedral, trigonal bipyramidal, seesaw

and deciding what looks like what

I remember realizing some pattern when I took gen chem like 2 years ago, but I have no idea what is is anymore

It had something to do with decreasing number of electron pairs or something like that and how the changing # of electron pairs influence bond angles, but I can't seem to figure it out anymore

Memorize all of the 'full' ones...tetrahedral, bipyramidal, etc...the rest are just those, but with pieces missing where there are LPs instead of atoms. They're usually pretty straightforward from the name/description, so if it's a multiple choice situation, you're set.

 

[Jepstein30]

VSEPR*

also, what the above guy said.

memorize the full forms and then figure out which bond angle is most strained and would be removed first to generate the 'degenerate' forms.

 

[mehc012]

VSEPR*

also, what the above guy chick said.

memorize the full forms and then figure out which bond angle is most strained and would be removed first to generate the 'degenerate' forms.

Haha, thanks, I somehow forgot to mention that little pet peeve of mine! VESPR is almost as bad as flouride in my book!

 

[ar00n]

If you try to visualize the arrangements of bond pairs and lone pairs with the goal of minimizing electron repulsion, I find the shapes make sense so long as you remember the electron geometry.

For examples, six electron pairs gives you octahedral geometry. Replacing any one of the bonding pairs with a lone pair would form a square pyramid. Then you can reason out that the shape with 4 bonding pairs and two lone pairs would be square planar since having two lone pairs across from each other would have less repulsion than any other shape you could think of. Try thinking about the other shapes you can form a couple times and it might be a little more intuitive.

This might be a start: http://www.chemguide.co.uk/atoms/bonding/shapes.html