GC: Polar vs Non Polar

[addis4ever]

OK....I'm really confused about determining which one is a more polar compound than the other... say for example:
Between BF3 and CH2Cl2, which one is more polar?

I choose BF3 because 1) the vectors don't cancel out, thus a polar molecule and 2) F is more electronegative than Cl. Is my reasoning right?

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[rpatel8]

BF3 is a non-polar molecule. If you draw out the lewis structure, there are no lone pairs and their is no dipole. CH2Cl2 is polar because when drawn out, the dipoles do not cancel

 

[LetsGo2DSchool]

BCl3 is trigonal planar. The three dipoles created by each Cl cancel each other out with this molecular geometry.

CH2Cl2 is tetrahedral. The dipoles do not cancel each other out in this molecule.

 

[AllahIsGreater]

also think of it easily like this. BF3 are there any DIFFERENT groups around the B? No they are all the same, thus non-polar (non-different)

 

[addis4ever]

BCl3 is trigonal planar. The three dipoles created by each Cl cancel each other out with this molecular geometry.

CH2Cl2 is tetrahedral. The dipoles do not cancel each other out in this molecule.

How do the three dipoles cancel each other out in BF3? u have 2 that do cancel out because they're going opposite directions, but what about the third one? thats where i'm confused. Also, i think i understand what dipole means; its when u have a partial positive and partial negative end when drawing the arrow right? If thats the case, then BF3 is def dipole because F is more electronegative than B. and u'll have the partially negative side on F and positive on B?

 

[addis4ever]

also think of it easily like this. BF3 are there any DIFFERENT groups around the B? No they are all the same, thus non-polar (non-different)

ok, so for future references, if the groups are all the same around the central atom then that's an automatic non-polar. am i right?

 

[AllahIsGreater]

ok, so for future references, if the groups are all the same around the central atom then that's an automatic non-polar. am i right?

thats how i think of it. also remeber this rule. whenever you do the geometry (like tetrahedral or triganol planar) whenever you have a BENT molecule, then its polar. For example H2O ....overall gemoetry is bent, thus its a polar molecule. remember these two rules. i believe this is the scope of the DAT.

 

[needzmoar]

ok, so for future references, if the groups are all the same around the central atom then that's an automatic non-polar. am i right?

Not always. If there is symmetry so that the dipole vectors cancel out, like inXeF4, then yes. A molecule can be surrounded by the same atoms and still be polar. SF4, for example, is polar.

 

[needzmoar]

edit:

 

[AllahIsGreater]

Not always. If there is symmetry so that the dipole vectors cancel out, like inXeF4, then yes. A molecule can be surrounded by the same atoms and still be polar. SF4, for example, is polar.

You have to read what i said, exactly. I said it cannot have ANYTHING DIFFERENT around the central atom. LOL YOU even confused me

 

[needzmoar]

You have to read what i said, exactly. I said it cannot have ANYTHING DIFFERENT around the central atom. Now looking at XeF4, when we draw it out, we have Xe with 4 F's around it, and 2 LONE PAIRS. are lone pairs and the F, the same exact thing? No. Thus its Polar. Listen to my method, its easy and wont lead you wrong. Once you draw out the structure look with your eyes, if there is anything "DIFFRENT" = POLAR!!!!!!!!!!!!

1) I was actually responding to the OP, I didn't see your post.
2) XeF4 is non-polar

I was just giving the OP an example of a non-polar molecule with lone pairs on the central atom. Chill, lol.

 

[AllahIsGreater]

1) I was actually responding to the OP, I didn't see your post.
2) XeF4 is non-polar

I was just giving the OP an example of a non-polar molecule with lone pairs on the central atom. Chill, lol.

lol im not mad lol....lol i think we just confused ourselves. i just believe on if they ask about polarity they would ask you which is most polar, so then just look for one where you have really electronegative elemtns like F and stuff.

 

[AllahIsGreater]

XeF2 is a linear molecule. The four unbound electron pairs balance. Non-polar.

XeF4 is planar, so again the two unbound pairs balance out. Non-polar.

CCl4 is tetrahedral with no unbound pairs. Non-polar.

PBr5 is a trigonal bipyramid with no unbound pairs. Non-polar.

BrF5 is octohedral, but at one bonding site is a free pair of electrons. The forces don't balance. This is the polar molecule.

 

[needzmoar]

lol im not mad lol....lol i think we just confused ourselves. i just believe on if they ask about polarity they would ask you which is most polar, so then just look for one where you have really electronegative elemtns like F and stuff.

ahh ok. I just wanted the OP to understand that it could be polar or non polar even if it's surrounded by the same atom.

XeF2 is a linear molecule. The four unbound electron pairs balance. Non-polar.

XeF4 is planar, so again the two unbound pairs balance out. Non-polar.

CCl4 is tetrahedral with no unbound pairs. Non-polar.

PBr5 is a trigonal bipyramid with no unbound pairs. Non-polar.

BrF5 is octohedral, but at one bonding site is a free pair of electrons. The forces don't balance. This is the polar molecule.

lol I just copied and pasted this into google..yahoo answers? ಠ_ಠ lol

 

[AllahIsGreater]

ahh ok. I just wanted the OP to understand that it could be polar or non polar even if it's surrounded by the same atom.


lol I just copied and pasted this into google..yahoo answers? ಠ_ಠ lol

yep. its a good explanation!

 

[addis4ever]

oh thanx guys! Now i really understand! much better...because before i was always going with my gut instinct and got it right but never truly understood it. it makes sense now.