Day 10: More Complex Molecular Structures

So far, our work with Lewis structures has focused entirely on hydrocarbons—molecules composed of just carbon and hydrogen. We’ve seen how carbon tends to form four bonds, how hydrogen forms only one, and how these patterns allow us to construct valid Lewis structures for stable molecules like methane (CH₄), ethene (C₂H₄), and propane (C₃H₈).

These cases reveal a broader pattern we often observe in stable molecules: many atoms (especially those in the second period of the periodic table) tend to be surrounded by eight electrons. This observation, sometimes called the octet rule, has strong predictive value. But it’s important to remember: the octet rule does not cause stability. In fact, some stable molecules violate it, and some molecules that follow it are still high in energy. Nevertheless, it’s an excellent place to start when constructing and evaluating Lewis structures.

But hydrocarbons are just the beginning.

Most biologically and industrially important molecules contain more than just carbon and hydrogen. Many include oxygen, nitrogen, or halogens like chlorine and fluorine. These elements bring their own typical bonding patterns and reactivity. Our Lewis model can handle these atoms too, but we need to expand how we apply it.

Let’s begin by remembering what a Lewis structure is: a two-dimensional symbolic model that helps us visualize atom connectivity and how valence electrons are shared or held as lone pairs. It’s not meant to show molecular geometry or the actual shapes of molecules—that’s something we’ll explore later. For now, we’re focused on connections and electrons.

Here are links to all sections of the work for Day Ten. Be sure to complete them before your whole-class meeting.

D10.1 New Atoms, Familiar Rules

D10.2 Bonds, Molecules, and Structures

D10.3 Line Structures

D10.4 Isomeric Structures

D10.5 Constitutional Isomers

D10.6 Functional Groups

D10.7 Electronegativity

Day Ten Podia Problem