What better way so show your love for your favorite chemist than with a space-filling molecular model of a molecule that just happens to look like a lacy valentine! Just think, if you were to give your true love a single gram of phenanthrene, they would have 3.4 x 10^21 valentines (albeit very small and difficult to personalize). Phenanthrene is easily available from most chemical supply houses (CAS 85-01-8), but it doesn't smell particularly nice, so you're probably better off just giving your sweetheart the model. Some folks may notice that I've chosen a non-traditional color for carbon; there's no rule that says that carbon has to be black.
10 CarbonPH6 in your choice of color
2 CarbonJPH1 in the same color
10 Hydrogen in a different color
24 bonds in any color
I've included some files grouping these objects if it helps.
The bonds are tight, so I have included a tool to help insert them. Join one CarbonPH6 to each CarbonJPH1 using the rectangular holes (the round ones go out). Snap these two assemblies together. Then join a hydrogen to each of two CarbonPH1's by the round holes and snap them to the top of the other assembly (there won't be enough room to add these hydrogens later). The hydrogens may be too close together, so you will probably have to sand them a little. Then make two groups of three CarbonPH6's using the rectangular holes and snap these to the sides of the other assembly. Add the remaining hydrogens to the remaining (hopefully round) holes and you're done.
If you now have an uncontrollable desire to make more molecules, you should probably critically evaluate your love life, however the following files are provided for the hopeless: the starter set (http://www.thingiverse.com/thing:1720048), the carbon expansion set (http://www.thingiverse.com/thing:1730299), the aromatic expansion set (http://www.thingiverse.com/thing:1754393), halogen expansion set (http://www.thingiverse.com/thing:1730099), nitrogen expansion set (http://www.thingiverse.com/thing:1753583), and sulfur and phosphorus expansion pack (http://www.thingiverse.com/thing:2350618)
I used ABS. Three perimeters works well.