There are many more than the six basic shapes in the database. Six additional common structural types are included in the "expanded valence" subset of the database. The term "expanded valence" comes from the idea that they require the use of d orbitals for their bonding, and, because of this, the central atom no longer needs to obey the "octet rule." (Noncentral atoms always obey the octet rule.)

The "expanded valence" section of the CoolMolecule database allows you to focus on these molecules. It does not include the very complex shapes that are included in the "full database."

Suggested Activity #1

Have students look at some molecules in the database that exhibit expanded valence. Choose some molecules from the list yourself and use them as an introduction to the concept of expanded valence. You can have the students make note of which atoms often have more than 8 electrons around them, and then tell them the general rule for determining if an atom is allowed to exhibit expanded valence. (Row 3 and lower on the periodic table.)

Suggested Activity #2

Consider having students make Molecular Origami paper models of the "expanded valence" shapes. (Look with structures that list "pdf" in the far column on the right.) It is often easier to connect the name with the shape if the student can hold it in his/her hand and see how, for example, the "see-saw" shape can pivot like a see-saw on their desk.