How is "CO"_2CO2 nonpolar?
1 Answer
By symmetry.
Polarity is a vector concept, i.e. a bond is polar because the electric dipole moment
vecmu = << mu_x, mu_y, mu_z >>→μ=⟨μx,μy,μz⟩
As vectors of identical magnitudes in exactly opposite directions add to cancel out completely, a "perfectly symmetrical" compound must be nonpolar, so that
sum_i vecmu_i = 0∑i→μi=0
For
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So, what do we mean by "perfectly symmetrical"? We mean the parent geometries of each so-called VSEPR structure, i.e. the ones with no lone pairs of electrons:
- two-atom linear, e.g.
"N"_2N2 - three-atom linear, e.g.
"CO"_2CO2 - trigonal planar, e.g.
"BF"_3BF3 - tetrahedral, e.g.
"CCl"_4CCl4 - trigonal bipyramidal, e.g.
"PF"_5PF5 - octahedral, e.g.
"SF"_6SF6 - etc.
all of which were NONPOLAR as listed above.
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The following, more usual examples, are POLAR:
"NO"^(+)NO+ , i.e.:"N"-=stackrel((+))("O": ):N≡(+)O: , two-atom linear"N"_2"O"N2O , i.e.:stackrel((-))ddot"N"=stackrel((+))"N"=ddot"O": , three-atom linear"AlF"_2"Cl" , trigonal planar"CH"_3"Cl" , tetrahedral"PF"_3"Cl"_2 , trigonal bipyramidal"SF"_5"Cl" , octahedral
