The first approach requires only that students are familiar with molecules represented as Kekulé structures such as those
shown in high school text books. The modeling lesson is used to further develop their understanding of this as a representation. This leads the students to the definition of a covalent bond as a shared pair of electrons leading to the use of the Lewis model. The second approach is used with students who already have some confidence in drawing Lewis “dot and cross” diagrams within the requirements of their examination syllabus and is useful as a revision lesson.