How to determine if a molecule is an ionic, covalent, or polar covalent bond?

For my test tomorrow, there will be molecules and I'll have to determine which type of bond they are. I know that ionic occur between a metal and nonmetal so NaCl would be one. I also know that covalent occurs between two alike or closely alike atoms like H2. I'm having a hard time determining polar covalent bonds because sometimes I can't figure out if the two atoms are more similar or more different in terms of electronegativity. My periodic table doesn't list the electronegativities so I won't be able to figure out the difference in energies. What should I do?