BF3-nonpolar?

[inaccensa]

How is BF3 nonpolar? The dipole moment extend from fluorine to boron. Although it has a trigonal planar geometry, but kaplan says its geometric structure helps cancel out the dipole moment. Can someone please explain this!!

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[RogueUnicorn]

dipole moments are vectors like force. is CH4 polar? the dipole moment extends from hydrogen to carbon.

 

[inaccensa]

dipole moments are vectors like force. is CH4 polar? the dipole moment extends from hydrogen to carbon.

But they are only 3 bonds here, how are the dipoles canceling? i understand the 2 of the bonds will cancel, but shouldn't there be a net dipole due to the 3rd bond.


http://en.wikipedia.org/wiki/File:Boron-trifluoride-2D-dimensions.png

 

[thebillsfan]

b/c boron doesnt have extra valence lone pairs. if it did then we'd have a problem. since it doesnt the molecule is planar, and the dipoles cancel out nicely.

 

[bacotell]

Imagine Boron is like a pole sticking vertically. Now think vectors. If I put three equal forces from people pulling on ropes tied to the pole (like the flourines), 120 degrees apart, (the same a trigonal planar) the pole wont move.
Run through a vector calculation with forces, youll see they all add up to zero.

 

[RogueUnicorn]

to answer your Q, read your post again -

How is BF3 nonpolar? The dipole moment extend from fluorine to boron. Although it has a trigonal planar geometry, but kaplan says its geometric structure helps cancel out the dipole moment. Can someone please explain this!!

 

[Omni]

Look at it like this.
You have a box and you are applying 20 Newtons of force to the left, right, top, and bottom. Every force cancels each other out.
In trigonal planar, the forces are 120 degrees apart and their i and j vectors cancel each other out.
Just do the math.

(cos0 + cos120 + cos240) x 20N =
(sin0 +sin120+ cos240) x 20N=

I haven't calculated it, but both will give you 0.
That was the mathematical way of looking at it.

 

[Phosphorus Ylide]

Imagine Boron is like a pole sticking vertically. Now think vectors. If I put three equal forces from people pulling on ropes tied to the pole (like the flourines), 120 degrees apart, (the same a trigonal planar) the pole wont move.
Run through a vector calculation with forces, youll see they all add up to zero.

 

[ChemEngSoonMD]

How is BF3 nonpolar? The dipole moment extend from fluorine to boron. Although it has a trigonal planar geometry, but kaplan says its geometric structure helps cancel out the dipole moment. Can someone please explain this!!

here is an easier question:
is O=C=O polar? You got a loooong ways to study...

 

[RogueUnicorn]

^^^ LOL@the avatar thief.

be nice.

 

[inaccensa]

Look at it like this.
You have a box and you are applying 20 Newtons of force to the left, right, top, and bottom. Every force cancels each other out.
In trigonal planar, the forces are 120 degrees apart and their i and j vectors cancel each other out.
Just do the math.

(cos0 + cos120 + cos240) x 20N =
(sin0 +sin120+ cos240) x 20N=

I haven't calculated it, but both will give you 0.
That was the mathematical way of looking at it.

Thanks that makes sense.