February 27, 2017

Homework Help: Chemistry-Polarity

Posted by Mary on Saturday, November 14, 2009 at 8:36am.

I am having trouble understanding polarity. I think I understand what it is - when a chemical bond occurs and there is or is not a resulting charge on the molecule. And the book says that the amount of polarity is the difference in the electronegativity between the two atoms in the bond (is my answer to the second question correct?).

What I don't understand is how to find the electronegativity, or even if the molecule has a dipole or not, if there are more than two atoms in the molecule. For instance, in the first problem, it says that CO2 is nonpolar. Why? H2O is polar, so obviously it isn't the structure of the atom that causes polarity, although our text uses the picture of children pulling on a rope in opposite directions to teach this concept. What am I missing? Thanks - this is so confusing!

First question: An individual carbon-oxygen bond is polar. Yet carbon dioxide, CO2, which has two carbon-oxygen bonds, is nonpolar. Why?

Second question: Which bond is most polar: H-N, N-C, C-O, C-C, O-H, or C-H?

The O-H bond would be most polar since it has the greatest difference in electronegativity.

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