Whats the difference between Molecular geometry and electron
Whats the difference between Molecular geometry and electron-pair (basic geometry)
for example NH4+ is sp3 hybridization on the atom the molecular geometry is a tretrahedral, but whats the difference with electron-pair (basic geometry)? I know sometimes its the same and sometimes its different. thanks for the help.
October 6, 2012
6 Comments • Newest first
@Chemo12 [url=http://imgur.com/Skdam.jpg]Drew out how to get SO2's Lewis structure here[/url]
Yes. You're right. It's bent shaped because of that electron pair above sulfur! Remember that lone pairs pull stronger than the electrons inside bonds do so this is why lone electron pairs distort the overall shape a bit.
You don't put double bonds on both sides because everything has an octet already with one double bond, one single bond, and one lone pair on sulfur.
[quote=rabbithole]Oh. I get what you're asking now.
The electron pair is talking about the bond angles between a terminal atom and the central atom. The molecular geometry takes into account all the angles together.
It differs because the molecular geometry describes what OVERALL shape it falls under (linear, tetrahedral, etc.). The electron pair geometry is describing it more specifically.
Try it with BF3. You'll see that since it has no electron pairs floating around, both the molecular geometry and electron pair geometry will be trigonal planar.
But if you try it with SO2, its molecular geometry will be trigonal planar but its electron pair geometry will be bent. This is because SO2 has three places with electron density: the two oxygens plus that one electron pair.
Hope this makes sense [/quote]
uh i tried BF3 and it works perfect but SO2 i messed up. SO2 has all together 18 electrons right? O S O oxygen has the greatest electronegativities so they get the 8 electrons each thats 16, so theres 2 more. I gave them to Sulfur so sulfur is sharing 4 and it has 2 above. so 6. since Sulfur also wants 8 i moved 2 electrons from Oxygen and gave it to Sulfur make it a double bonded on one side. Then they all have 8. and its 18 electrons. But thats not angular bent is it? Is the 2 electrons from above the sulfur? or should i make it double bonded on both sides? Woulnt that make it linear or with the 2 electrons out would it be linear or angular bent?
omg sooo confusinggg! sorry if it dosent make any sense.
Oh. I get what you're asking now.
The electron pair is talking about the bond angles between a terminal atom and the central atom. The molecular geometry takes into account all the angles together.
It differs because the molecular geometry describes what OVERALL shape it falls under (linear, tetrahedral, etc.). The electron pair geometry is describing it more specifically.
Try it with BF3. You'll see that since it has no electron pairs floating around, both the molecular geometry and electron pair geometry will be trigonal planar.
But if you try it with SO2, its molecular geometry will be trigonal planar but its electron pair geometry will be bent. This is because SO2 has three places with electron density: the two oxygens plus that one electron pair.
Hope this makes sense
EDIT: I'd write it down. This helps prove my point better.
linear: sp, 0 lone pairs, linear geometry, like CO2
trigonal planar:
0 lone pairs, trigonal planar geometry, like BF3
1 lone pair, bent geometry, like in SO2
tetrahedral:
0 lone pairs, tetrahedral, like CH4
1 lone pair, trigonal pyramidal, like in PCl3
2 lone pairs, bent, like H2O and OF2
trigonal bipyramidal:
0 lone pairs, trigonal bipyramidal, like PCl5
1 lone pair, folded square, seesaw, SF4
2 lone pair, T-shaped, ICl3
3 lone pair, linear, XeF2
octahedral:
0 lone pairs, octahedral, SF6
1 lone pair, square pyramidal, BrF5
2 lone pairs, square planar, XeF4
Notice how everything with 0 lone pairs has the same molecular geometry as its electron pair geometry.
@Chemo12
ok i dont really know how to explain it properly but heres a photo from my worksheet
http://imageshack.us/photo/my-images/145/picture11j.jpg/
its the electron-pair basic geometry sometimes its the same sometimes its different but i dont understand why.
What are you asking?
I don't quite understand what you're asking, but you get the molecular geometry using Lewis structures.
If you're asking why NH4+ is tetrahedral, you describe the molecular geometry based off the central atom (the least electronegative).
By electron pair, are you referring to formal charge or resonance or something?
Maybe a rephrase would help.