Note that wax crumbles but sodium chloride cleaves in smooth planes. Relate this to a difference in bond type. Given a number of formulae for covalent compounds, students build models to represent the bonding. Students could begin by deducing from an element's position in the periodic table the number of bonds it is likely to form. Knowing the bonding behaviour of an element, students can determine the possible structure of a set of atoms.
Students can also draw electron dot diagrams.
Bonding theory helps explain why certain properties appear and how to predict the properties of new substances. Use toothpicks for both ionic and covalent bonds. In addition, check simple polyatomic ions for correct charge. Provide a model so students can check their work for accuracy. As students work on the questions, circulate, asking selected students to talk about what they are doing, to define the term valence electron, and to describe the role electrons play in both covalent and ionic bonding.