1. If polar bonds are symmetrically oriented, the molecule is nonpolar.
QUESTION:
Which of the following molecules is polar? A. H2O, B. BF3, C. CH4, D. PF5
A polar molecule must have at least one polar bond. CH4 has no polar bonds. C-H bonds are nonpolar.
If polar bonds are symmetrically oriented, the molecule is nonpolar.
Polar B-F bonds in BF3 are symmetrically oriented.
Polar P-F bonds in PF5 are symmetrically oriented.
Polar O-H bonds in H2O are not symmetrically oriented.
Which of the following molecules is polar? A. H2O, B. BF3, C. CH4, D. PF5
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A polar molecule must have at least one polar bond. CH4 has no polar bonds. C-H bonds are nonpolar.
Therefore choice C is incorrect.
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If polar bonds are symmetrically oriented, the molecule is nonpolar.
Polar B-F bonds in BF3 are symmetrically oriented.
Therefore, choice B is also incorrect.
Polar P-F bonds in PF5 are symmetrically oriented.
Choice D is also incorrect
THe correct answer is choice A.
Polar O-H bonds in H2O are not symmetrically oriented.
As a result, a water molecule is polar.
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2. BF3 has nonpolar bonds but is nonpolar
Here’s a model of the boron trifluoride molecule.
It is trigonal planar. All the B-F bonds lie on the same plane and are pointing towards the corners of an equilateral triangle.
Even though the B-F bonds are polar, they are symmetrically oriented.
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CLICK The polarities cancel out and the entire molecule is nonpolar.
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3. PF5 has polar bonds, but is nonpolar.
Here’s a model of the phosphorus pentafluoride molecule.
It is trigonal bipyramidal. All the B-F bonds are polar, but because of their symmetrical orientation, the molecule is nonpolar.
Imagine one PF bond as pointing to the north pole.
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Its polarity is cancelled by another PF bond pointing to the south pole.
CLICK Here’s a view of the molecule from the top, so you can see the symmetry of the other three BF bonds.
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The three equatorial B-F bonds are on the same plane and are 120 degrees apart.
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4. H2O has polar bonds and is polar.
Here’s a model of the water molecule.
It is a bent molecule. Both O-H bonds are polar and the molecule is polar.
Here’s the polarity of one OH bond. Note that the arrow is drawn pointing towards oxygen. Oxygen is more electronegative than hydrogen.
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And here’s the polarity of the other OH bond.
You can see that, overall, electrons are polarized towards the oxygen end of the molecule
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5. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08