NH3 and BCl3, polar/nonpolar?

[gomigomi]

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hello all,
i am taking the exam in the first week of july and currently i am working on the destroyer.

just wanted to ask, if any of you know why NH3 is polar and BCl3 is nonpolar.

thanks in advance! 🙂

 

[herkulease]

Boron only has 3 valence electrons.

when bonding to the chlorides the best configuration that maximizes the distance bt them is a trigonal planar. they are all 120 degrees apart and the "pull" each exert is balanced out.

Nitrogen has 5 electrons in NH3 it has 2 lone pairs. The lone pairs essentially create a dipole moment. If you have a dipole moment its going end up being polar. exactly how polar something is depends on other factors.

I think orgoman suggests drawing them out. I know it can be time consuming on the test if you don't remember common ones. But you would hate to miss an easy question.

 

[Ibracadabra]

Boron only has 3 valence electrons.

when bonding to the chlorides the best configuration that maximizes the distance bt them is a trigonal planar. they are all 120 degrees apart and the "pull" each exert is balanced out.

Nitrogen has 5 electrons in NH3 it has 2 lone pairs. The lone pairs essentially create a dipole moment. If you have a dipole moment its going end up being polar. exactly how polar something is depends on other factors.

I think orgoman suggests drawing them out. I know it can be time consuming on the test if you don't remember common ones. But you would hate to miss an easy question.

I think he explained it well, I'll add in some additional information.
NH3's lone pairs "push" the other covalent bonds down, so it essentially makes a trigonal pyramidal shape with angles 107.5 degrees. For polarity, you might want to look if: 1) Are there are different atoms attached to the central atom? if no, it should be polar; if yes, ask 2) is the molecule symmetrical? if no, it should be polar.

NH3 has the same cov bonds N-H bond attached to Nitrogen, however, the molecule is not symmetric. Therefore it is polar.

For BCl3, you must know that it is in group 3 with 3 valence electrons, and that Boron is usually considered to be the exception that's okay with not completely filling the octet(8 val. e-). BCl3 does fit 1) and 2), since it is trigoal planar with 120 degrees apart.

Hope it helps!😀

 

[Baylor2011]

The previous two already provided detail into your question, I'm going to suggest you take a look at molecular structures, you definitely need to get those nailed down.

One of the advantages to knowing the structures molecules make, is you can assess whether things are polar or not.

 

[gomigomi]

THANKS guys!
it makes sense now!
you guys are so awesome!!!