We suggest having students explore the "entry level" database,
taking special note of variation in bond length between molecules.
The "bonds" search was developed especially for this use.
Once the "bonds" search is selected, the red histogram on the left can be used to narrow
down the search to show only molecules that contain bond lengths within a certain range.
It is difficult to see the pattern if the whole database is searched, so we suggest using the "entry level"
database and restricting the search to CC, CN, or CO bonds.
Students should be making sigma structures of some molecules on the list,
and a classroom discussion could follow about why some of the bonds
are so much shorter than others. At that point, the octet rule for the central atom can be introduced, and students can learn to draw full Lewis structures.
See the Construct a Lewis Structure web page for detailed, step-by-step information about converting sigma structures to Lewis structures.