So my A.P. Chem exam is tomorrow, and it just really freaked me out that my review books just claimed that O3 is polar. How is that possible? There can't be a difference in electronegativity between the same atom within a molecule, can there? I just figured it will have a strong-ish dipole moment due to a strong-ish London Dispersion Force because of the number of electrons but WHAT THE HELL. Sorry, I'm pretty stressed and this is really bugging me.
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Well, ozone has two resonance forms, each with a double bond, and each with a nonbonding pair of electrons on the central atom, thereby 'squishing' the shape of the molecule into a 'bent' molecular geometry. As you know, the bent geometry results in a net dipole moment, and thus, ozone has a dipole moment, and thus, is polar.
Dipole moments are VECTOR quantities; they have both a MAGNITUDE and DIRECTION. Electronegativity (magnitude) is one part of the issue of a dipole moment, but so are the positions (direction) of the atoms. You were right about the electronegativities being the same for all three oxygen atoms, but the position of the oxygen atoms also plays a key role in the issue of ozone being a polar molecule. Hence, draw the Lewis structure, note the differences in electronegativities of the atoms, note their position, and finally, note whether they cancel each other out.
Don't worry about dipole moments too much, since most of the AP Chemistry exam focuses on reactions and equilibrium. At least that's the way it was for me when I took it 4 years ago. Anyway, good luck.
Dipole moments are VECTOR quantities; they have both a MAGNITUDE and DIRECTION. Electronegativity (magnitude) is one part of the issue of a dipole moment, but so are the positions (direction) of the atoms. You were right about the electronegativities being the same for all three oxygen atoms, but the position of the oxygen atoms also plays a key role in the issue of ozone being a polar molecule. Hence, draw the Lewis structure, note the differences in electronegativities of the atoms, note their position, and finally, note whether they cancel each other out.
Don't worry about dipole moments too much, since most of the AP Chemistry exam focuses on reactions and equilibrium. At least that's the way it was for me when I took it 4 years ago. Anyway, good luck.