[Frater EIE]

Hey

Not sure if this would be categorized as a  highschool chem question or not, but here goes:

I'm reading through Clifford C. Houk and Richard Post's Chemistry: Concepts and Problems and ran into what seems to be a contradiction. It described an H₂O molecule as being "bent" (as well as planar), so that the "tugs" (the pull on the electrons) do not offset each other, making the molecule polar. A nonpolar molecule would be a linear one, since, as it described just before, it would be like two teams playing tug-of-war, pulling on a rope, with neither team moving, i.e. nonpolar.

Almost immediately after that, it says "Planar molecules are nonpolar". Well, I thought that depended on it being linear or not. So then it goes on and describes S0₃ as a planar, nonlinear (i.e. bent) molecule. Obviously it would be polar

Au contraire, it says it is nonpolar...  This makes no sense Can somebody please help this befuddled brain?

[TheJoker]

ya ha this is a little bit confusing. yeah H20 is obviously polar, like you said, because the tug on the electrons from the atoms are not all the same, making the molecule polar.

on the other hand, when you are thinking of a nonpolar molecule always being linear, that is not always the case. Like if you draw the structure of a CO2 molecule, you know its non polar because it is like the "people playing tug o war" like you described.   
If you draw the lewis dot structer of SO3 though, even though it is not linear (it is planar) the tug from all of the Oxygen atoms is equal, even though there are three of them. This makes the molecule nonpolar.

Also keep in mind that a molecule can have have polar bonds, and can be a nonpolar molecule, like CCl4. Even though each bond is polar, they cancel each other out and for a cross shape, which you can see is nonpolar.  It is the same with the SO3 molecule.

[TheJoker]

i hope that kinda helped haha

[Frater EIE]

Thanks, that does make some sense. I guess then I'm confused about how to figure out if the tug of the combined bonds is equal or not. Can you please explain? And why did it say "Planar molecules are nonpolar" when that's obviously not always the case?

[TheJoker]

hey whatsup,

so you said you were confused about whether the tug of the all the bonds combined is equal or not? Thats a good question. First, I look at it from a simple standpoint. If the molecule is symmetrical (like CO2 or CCl4) then the tugs are equal.
Also, you have to look at which atoms around the central atom are "tugging" the electrons. This is where a thing called "electronegativity" comes into play. Electronegativity is basically an atom's tendency to attract atoms towards itself. For example, Fluorine has the highest electronegativity because it essentially wants electrons the most to make it stable (the F- ion). Does that make sense?

So, keeping this in mind, take the molecule CH3Cl. If you draw it, its just a "cross" with the C in the middle bonded to 3 H's and 1 Cl. Even though the molecule looks symmetrical, the Cl wants electrons more it makes the molecule polar. So you have to look at which atoms are tugging the electrons.

I hope I didn't confuse you more haha

[TheJoker]

** Oh and electronegativity is an atom's ability to attract ELECTRONS   towards itself, not atoms like I put in my last post. Sorry about that.

[Alquimista]