Chem 101 exam tomorrow, what the fuck is molecular geometry?

>>8524563
>Seriously Vsepr pairs and all that shit seem like they should be relativity easy to understand

OK, VSEPR takes into account both lone pairs and bonding electrons.
Molecular geometry is concerned only with the latter.
This is why water is 'bent' but methane is 'tetrahedral', in terms of geometry.

Well you need to know how to properly make a Lewis structure. If there are multiple resonance structures pick the one that has the least amount of formal charges and that has the formal charge(s) on the most electronegative atom.

Then once you made the Lewis structure count the electron domains. An electron domain is a bond between atoms and a lone pair of electrons on the central atom. Once you do that consult your molecular geometry chart (you might need it memorized for finals) and pick the geometry that corresponds to the amount of bonds/lone pairs you have.

>>8524587
Also forgot to mention that atoms on row 3 or greater are able to have more than an octet. Rows 1 and 2 cannot.

>>8524577
>This is why water is 'bent' but methane is 'tetrahedral', in terms of geometry.
I wouldn't talk to him about that unless you're going to mention how electron fields work

Man, this question already tormented me. If you already made the lewis structure and it is correct, just count the number of single bonds and electron pairs! Also, there's no molecule with sp4 hybridization because there are only 3 orbitals p.

>>8524593
>row 3 can have higher than an octect
>lowest formal charge

That actually makes it much clearer, so thank you. Throughout the class the professor never bothered to explain the Lewis structures they were drawing to determine the geometries, just filled all the octects and threw the extra lone pairs on the center without much context, so it never clicked for me.

So the geometries aren't exactly intuitive, more over memorization?

>>8524624
Yeap, it's about memorization! But it helps if you used 3D models and see the geometric figures behind the molecule and vice-versa.

Jesus its not memorization its based on the maximization of distance for between the atoms ie placing 4 atoms bonded to a single central atom results in the tetrahedral shape. This is super easy shit, find a good table and learn the shapes 2,3,4,5,6 is linear, trigonal planar, tetrahedral, trigonal bypyramidal and octahedral respectively. Substituting lone pairs for atoms slightly changes the shape. Just google it and find a good reSourxe VSEPR is simple, really.

>>8524624
>>8524651
If you're trying to memorize VSEPR you're a brainlet desu

All you have to do is maximize the distance between 'things' on the atom