VSEPR Theory = Massive Confusion?

[wired202808]

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Can someone please explain how I'm supposed to either learn this or memorize it? Chad has a long list of stats but I'm not sure how to understand this so I can know it vs. cramming it (because its not sticking anyway.) Like do I have to know the EDG and MG of every single hybridization?

 

[Juggernauts]

EDG only deals with the number of domain numbers around the central atom.
2 domains = linear shape= sp
3 domains = trigonal planar shape = sp2
4 domains = tetrahedral shape = sp3
5 domains = trigonal bipyramidal shape = sp3d
6 domains = octahedral shape= sp3d2

MDG takes into account the #of bonds + the #of non-bonding e' pairs to make up the domain number.
2 domains = 2 bond + 0 nonbonding e' = linear shape = sp
3 domains = 3 bond + 0 nonbonding e' = trigonal planar shape = sp2
3 domains = 2 bond + 1 nonbonding e' pair = bent shape = sp2
4 domains = 4 bond + 0 nonbonding e' = tetrahedral shape = sp3
4 domains = 3 bond + 1 nonbonding e' pair = trigonal pyramidal shape = sp3
4 domains = 2 bond + 2 nonbonding e' pair = bent shape = sp3 (think water)
5 domains = 5 bond + 0 nonbonding e' pair = trigonal Bipyramidal = sp3d
5 domains = 4 bond + 1 nonbonding e' pair = seesaw = sp3d
5 domains = 3 bond + 2 nonbonding e' pair = T-shaped = sp3d
5 domains = 2 bond + 3 nonbonding e' pair = linear = sp3d
6 domains = 6 bond + 0 nonbonding e' pair = octahedral = sp3d2
6 domains = 5 bond + 1 nonbonding e' pair = square pyramidal = sp3d2
6 domains = 4 bond + 2 nonbonding e' pair = square pyramidal = sp3d2

After looking at this mess, I don't know if that helps explain or not. Really, the trick is to draw each shape and account for the bonds and nonbonded electron pairs. If you still have your Gen Chem book, I would think it is all laid out pretty well in the beginning chapters. Sorry if I added to your confusion. But one thing to recognize is that the names are the same for EDG and MDG if there are no nonbonded electron pairs.

 

[wired202808]

EDG only deals with the number of domain numbers around the central atom.
2 domains = linear shape= sp
3 domains = trigonal planar shape = sp2
4 domains = tetrahedral shape = sp3
5 domains = trigonal bipyramidal shape = sp3d
6 domains = octahedral shape= sp3d2

MDG takes into account the #of bonds + the #of non-bonding e' pairs to make up the domain number.
2 domains = 2 bond + 0 nonbonding e' = linear shape = sp
3 domains = 3 bond + 0 nonbonding e' = trigonal planar shape = sp2
3 domains = 2 bond + 1 nonbonding e' pair = bent shape = sp2
4 domains = 4 bond + 0 nonbonding e' = tetrahedral shape = sp3
4 domains = 3 bond + 1 nonbonding e' pair = trigonal pyramidal shape = sp3
4 domains = 2 bond + 2 nonbonding e' pair = bent shape = sp3 (think water)
5 domains = 5 bond + 0 nonbonding e' pair = trigonal Bipyramidal = sp3d
5 domains = 4 bond + 1 nonbonding e' pair = seesaw = sp3d
5 domains = 3 bond + 2 nonbonding e' pair = T-shaped = sp3d
5 domains = 2 bond + 3 nonbonding e' pair = linear = sp3d
6 domains = 6 bond + 0 nonbonding e' pair = octahedral = sp3d2
6 domains = 5 bond + 1 nonbonding e' pair = square pyramidal = sp3d2
6 domains = 4 bond + 2 nonbonding e' pair = square pyramidal = sp3d2

After looking at this mess, I don't know if that helps explain or not. Really, the trick is to draw each shape and account for the bonds and nonbonded electron pairs. If you still have your Gen Chem book, I would think it is all laid out pretty well in the beginning chapters. Sorry if I added to your confusion. But one thing to recognize is that the names are the same for EDG and MDG if there are no nonbonded electron pairs.

this helps! i have my old book i have to find it and use it! but how did you remember all of this info?

 

[punchdrunk7]

Best advice is to watch Chads videos, he taught me chemistry all over again. He is the man.

 

[wired202808]

punchdrunk i did watch them, actually thats why im question it is because i have huge chunk of info from that his pdf files i just want to know how to synthesize it. i guess ill watch that video over again.

 

[To be MD]

EDG only deals with the number of domain numbers around the central atom.

MDG takes into account the #of bonds + the #of non-bonding e' pairs to make up the domain number.

For anyone reading this, I'd like to add that this formula is not "# of bonds" but, rather, # of sigma bonds.

The correct formula would be: #of sigma bonds + #of non-bonding e' pairs to make up the domain number

Thus, the central carbon in acetone below is sp2 hybridized. We get that from 3 sigma bonds + 0 non-bonding lone pairs = trigonal planar & sp2. (..whereas if you used # of bonds in general, you would get 4 + 0 which would make you think this carbon is sp3)

 

[DAT Destroyer]

Can someone please explain how I'm supposed to either learn this or memorize it? Chad has a long list of stats but I'm not sure how to understand this so I can know it vs. cramming it (because its not sticking anyway.) Like do I have to know the EDG and MG of every single hybridization?

Your question is a very broad one indeed. Molecular geometry and hybridization is very important for the DAT exam. Forget any tricks.....learn it the correct way. The text by Raymond Chang simplifies this section greatly. Once you have this down, practice questions will reinforce the concepts. Experience has taught me that shortcuts lead to DISASTER.

Hope this helps..

Dr. Romano