(Polar molecules, Non-polar molecules, etc.)
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Knowing whether or not a molecule is polar depends on your knowledge of the structure first. Since there are 5 Cs in the molecule, it's a good indication that C5H5N will be form a ring-like structure such as benzene. However, instead of a 6th C, there is an N that completes the ring. Also, we know based on the Lewis structure that there must be a set of lone pairs (two electrons) on the N atom. We can assess from here that since N and C have different electronegativities, you can already make the conclusion that the dipole moment will be either toward the N or away from the N, without even knowing which atom is more electronegative. Since this is the case, the molecule has to be polar. Another way of thinking about polarity is to consider the lone pair on the N. Because it is there, we know that H ions can form H bonds with water, which is a polar molecule. That C5H5N, pyridine, can interact with water in this way is another indication that it is a polar molecule.
Sometimes good indicator of non-polarity can be symmetry! This is seen in naturally occurring Oxygen (O2) and Nitrogen (N2), as they are symmetrical no matter which way you look at the molecule. The same for a compound like CCl4, where the bonds look the same no matter what. These are examples of nonpolar molecules. If the molecule is not symmetrical, odds are it is polar.
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