How can I tell if a substance is Metallic, ionic, covalent molecular or covalent network?

take the difference of the electronegativities between the two elements involved and there's a table that tells you the percent ionic character. if the % is low, then it is most likely to be covalent, if it is high then it is ionic. what about those near the 50% region, well, i'm not sure how they clify those materials.