I would first get the student to find the elements on the Periodic Table, and work out how many valence electrons each atom had. Then I would get them to draw the structures of hydrogen and chlorine using the dot and cross diagram method (showing only the valence electrons). The student would then need to work out the type of bonding in the molecule, and we could briefly discuss ionic and covalent bonding (here it would be covalent bonding). The HCl molecule could then be drawn, using the dot and cross method. I would then ask the student how they knew if they were right, and speak about having a full valence shell after bonding.