This lab can be found in Matter and Change by Delta Science Modules. The lab goes much deeper than my 6th graders need to go, so I just do the part of the lab where the students make the molecules.
I gave each group a tray with the needed supplies along with their lab sheet. The lab sheet talked about how molecules come together and showed pictures.
Then the students made their molecules (6 total).
This is a ammonia.
This is carbon dioxide.
The students really enjoyed putting these together and asked if they could create more. I'll have to see what I can come up with for next year's group.