To be polar you must have these TWO items (both of them). Just one won't do.
a. You must have polar bonds meaning that the two atoms must have different electronegatives.
b. The molecule must NOT be symmetrical (in 3D space).
For example, CH4 has polar bonds because the electronegativity (EN) of C is 2.5 and that of H is 2.1 so there is a SLIGHT polarity and that satisfies #1.
But #2 is not satisfied because CH4 is a tetrahedral molecule so the polarity of the four individual polarized bonds is off set.
BUT look at CH3Cl. Each C-H bonds is polar; the C-Cl bond is polar but not the same as the C-H bonds. The molecule is tetrahedral but because one bond is different (the C-Cl bond) this molecule as a whole is polar.
Another example. CH4 vs NH3
CH4 is not polar for the reasons outlined above. What about NH3?
Each N-H bond is polar because EN for N is about 3 and H is 2.1 However, when you look at the NH3 molecule it is trigonal planar with those two unpaired electrons sitting on top. See this.
https://www.google.com/search?q=molecular+structure+NH3&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb
That is a non-symmetrical molecule so it satisfies both 1 and 2 and it is polar.
In your question, all of the molecules are linear. It tells you that in the question.
HCN the delta EN for C-H is not the same as the delta EN for C-N so those two polar bonds (in opposite directions) don't cancel and the molecule is polar.
CO2. The left C-O bonds is polar; the right C-O bond is polar and the exact polar bonds in exactly opposite directions cancel so CP2 is not a polar molecule.
N-N can't be polar There is no delta EN.
HCl, of course, is a polar molecule.
Hope this helps. Follow up if this is not clear.
which of the following linear molecules is a nonpolar molecule containing polar bonds?
H-C=N between C and N are three lines
O=C=O
H-Cl
N=N between N and N are three lines
Please explain... I am having a hard time comprephening this stuff.
Thanks
2 answers
In the NH3 example I gave I called that a trigonal planar molecule; I should have named it a trigonal pyramidal molecule.
1 answer