Figure 2.6 Covalent Bonding Can Form Compounds (A) Bohr models showing the formation of covalent bonds in methane, whose molecular formula is CH₄. Electrons are shown in shells around the nucleus. (B) Three additional ways of representing the structure of methane. In a structural formula, a covalent bond can be indicated with a single line or a shared pair of electron dots. The ball-and-stick model and the space-filling model show the spatial orientations of the bonds. The space-filling model indicates the overall shape and surface of the molecule. In the chapters that follow, different conventions will be used to depict molecules. Bear in mind that these are models to illustrate certain properties, not accurate portrayals of how atoms would actually appear.