10/7/2014
ALEKS Alex H. Yuan - 10/07/2014 7:45:20 PM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
Alex H. Yuan - 10/07/2014 7:45:20 PM EDT
General Chemistry (First Semester) / Chem 110 FA 2014 – CH110 FA14 S25-36 (Dr.
Barber)
1.
Predicting whether molecules are polar or nonpolar
Decide whether each molecule or polyatomic ion is polar or nonpolar.
If the molecule or polyatomic ion is polar, write the chemical symbol of the atom closest
to the negative side. For example, if the molecule were
and you decided the
hydrogen atom was closest to the negative side of the molecule, you'd enter " " in the
last column of the table.
molecule or
polyatomic ion
polar or
nonpolar?
atom closest to
negative side
polar
N2
nonpolar
N H3
+
N O2
polar
nonpolar
polar
nonpolar
Molecules can only be polar if some of the chemical bonds in them are polar:
The
molecule is nonpolar because the
bond is nonpolar.
The
bond is nonpolar because the valence electrons in it are
shared equally by the two hydrogen atoms.
The
polyatomic anion is polar because the
bond is
polar. The
bond is polar because the valence electrons in it
are pulled towards the more electronegative oxygen atom.
Molecules or polyatomic ions with one chemical bond, like
or
are always polar
when their chemical bond is polar, and always nonpolar when it's not.
However, molecules and polyatomic ions with more than one chemical bond can be
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ALEKS Alex H. Yuan - 10/07/2014 7:45:20 PM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
nonpolar even if all the bonds in them are polar. It all depends on how the bonds are
arranged. If the polar bonds are identical and arranged perfectly symmetrically, they will
cancel each other's influence, and the molecule will be nonpolar:
The
molecule is nonpolar, even though both
bonds are polar, because the electronegative
atoms pull the valence electrons exactly equally
and in exactly opposite directions.
The
molecule is polar. The electronegative
and atoms pull the valence electrons in opposite
directions but the
atom pulls harder, since oxygen
is more electronegative than sulfur.
The
molecule is nonpolar, even though all four
bonds are polar, because the electronegative
atoms pull the valence electrons exactly equally
and exactly symmetrically.
(You can rotate the molecule to get a better view by
dragging the slider with your mouse.)
To predict whether or not a molecule or polyatomic ion with more than one chemical bond
is polar, you'll need to combine your ability to predict whether or not chemical bonds are
polar with your ability to predict the shape of a molecule.
Now let's apply these general ideas to the particular problems you've got.
The dinitrogen
molecule has only one chemical bond, a nitrogen-nitrogen triple
bond. Since the two nitrogen atoms share the valence electrons in the
equally, this bond is not polar, and neither is the
The ammonia
≡
bond
molecule.
molecule has a trigonal pyramidal (triangular pyramid) shape.
Even though the nitrogen-hydrogen single bond are identical, they're not arranged
symmetrically, so this molecule will be polar:
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(You can rotate the molecule to get a better
view by dragging the slider with your mouse.)
The most electronegative atom in the molecule is the nitrogen atom, so the valence
electrons will be pulled to the
side of the molecule, and that side will end up
slightly negative.
The nitronium
cation is linear. That is, all three atoms lie in a straight line.
Although the nitrogen-oxygen double bond are polar, they are identical and point in
exactly opposite directions.
That means they completely cancel each other's effects, and the
cation is
nonpolar.
Here is the completed table:
molecule or
polyatomic ion
polar or
nonpolar?
atom closest to
negative side
polar
N2
nonpolar
N H3
+
N O2
polar
nonpolar
N
polar
nonpolar
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10/7/2014
ALEKS Alex H. Yuan - 10/07/2014 7:45:20 PM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
Copyright © 2014 UC Regents and ALEKS Corporation
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