More Complicated Molecules

In the Periodic Table, the positions of the columns indicate how many atomic bonds can usually be formed, as follows:

For C, N, O (in white to the right - these are the most important atoms for life):
  • C forms four bonds, (same for Si, Ge, ...)
  • N, P, As, ... (usually) form three (NH4+ is an interesting exception),
  • O, S, Se, ... form two,
  • H forms one (as seen above),
  • He, Ne, Ar, Kr in the rightmost column form 0.
This rule is shown by the combinations of H with C, N, O:
CH4: 4 H's can attach to C, forming methane
NH3: 3 H's can attach to N, forming ammonia
OH2: 2 H's can attach to O, forming water, usually written H2O

The Shapes of Molecules

To make the shapes of the molecules named above as realistic as possible, the angles between the H's should be right. Methane's H's are at the 4 points of a tetrahedron, and ammonia and water are very similar (but with some vertices not having H's).
You can make a cardboard guide showing where to stick the
toothpicks into the styrofoam spheres by folding a cardboard
tetrahedron of just the right size (2*61/2 times the diameter
of the sphere) around the sphere,...
then skewer it through the centers of the bottom face and 1, 2,
or all 3 of the other faces (note the slit for folding the face away from
the sphere without having to remove the toothpick)...
resulting in something like this:

For Oxygen, only 2 toothpicks would be used, for Nitrogen, 3; if double bonds are planned, pull out the toothpicks involved and replace with pipecleaner segments.
Next