This question was in my book. According to me CO should be polar as it should have a dipole moment.
But I found that the $\sigma$-electron drift from C to O is almost nullified by the $\pi$-electron drift from O to C. What is about the $\pi$-electron drift towards the Carbon atom?
In Google it is given CO is polar, but my book says it is practically nonpolar ... now I am confused.
Answer
Well, it's just like you said: $\sigma$ electrons drift from C to O, because O is more electronegative, and $\pi$ electrons drift in the opposite direction, because... Look at it this way: C and O are both sp, each with a lone pair facing away from the other atom. They form a $\sigma$ bond and a $\pi$ bond, too. Now they want to form another $\pi$ bond, but C got no more electrons to use, so O has to throw in two of his own. That's the drift we are talking about.
As it happens, the two effects almost negate each other. The resulting dipole moment is so insignificant, I don't even remember which way it is.
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