A suitable starter for the lesson would be a visual stimulus of a number of Kekuléstructures of simple molecules, leading to a discussion about what the line represents and the definition of a covalent bond, and linking this to the number of valence electrons for the atoms. The teacher is then able to lead the class in how a model can be built of the covalent bonding using pipe cleaners and beads, illustrating this with a simple molecule such as HCl as shown in