Watch this 8 minute video that gives lots of examples of polar and nonpolar covalent bonds versus ionic bonds. The teacher, Mr. Anderson, is very clear in his explanation of how to figure out the kinds of bonds that different molecules have. The videos are made by a high school science teacher who has made many, many videos about various science topics. After you know all you can from his Chemical Bonds video, check out some of the others.
courtesy of Knovation