Covalent versus ionic

Something that we haven't spent a lot of time on is the defintion of covalent bonding and covalent compounds.  For our purposes, compounds made from opposite ends of the periodic table are ionic.  They have a metal and a non-metal.  Covalent compounds are made from two non-metallic elements.  So, they are formed on the same end of the periodic table.  Carbon dioxide is a covalent compound, while lithium oxide is ionic.  Both contain oxygen, but only the latter contains a metal.  Keep this in mind when trying to decide between ionic and covalent bonds.