"I think that the most important characteristic of molecules is their shape. Shape is the crucial feature of chemistry, from its simplest interpretation - atomic radius (which governs the physical and chemical properties of the elements) - to its astonishing role in determining the function of biological macromolecules such as the proteins and nucleic acids. Understand the consequences of shape, and you understand the properties of matter."
We don't often approach chemistry from the point of view of shape. Here is a diagram that combines bond types (metallic, covalent, ionic) with dimensionality of the chemicals that are formed.
Here's a printable version of the tetrahedron. If possible, print it on cardstock, in color, 11"x17" (size A3 in Europe). For a smaller version, print it out letter (8.5"x11") and glue it to a manilla envelope.
While designed as more of an architectural activity, this toothpick-gumdrop activity is great for modeling how atoms can configure themselves in lots of different shapes.Details
Carbon can form many different structures by itself. Thought of dimensionally, a Buckyball is a "zero-dimensional" (0D) molecule, a carbon nanotube is 1D, a flat sheet of graphite is 2D, and a diamond is 3D. Paper printouts and chicken wire are good for modeling 0D, 1D, and 2D.Details
Diamond is carbon in 3D. This model uses pipe cleaners (chenille sticks) to build up the network solid.Details
This activity has a good model of 1D structures -- long polymer chains.Details
This is one of the nine central ideas that Peter Atkins lays out in his 2005 article, "Skeletal chemistry." Each of the other ideas has its own list in SMILE.