Giant beaded buckyball

I went to the 109th anniversary of TFGH yesterday and took a photo of this interesting giant buckyball.

Styrofoam ball/rubber band model of ethylene

I posted a bead model of ethylene made by Qing Pang, a high-school student in TFG school. I don't like the way double bond is handled in her model because the channel (hole) orientations of two beads that used to model double bond is perpendicular to the bond orientation. I would prefer to have a bead valence model in which channel of each bead lies exactly along a particular bond. In the sense, to describe a double bond by beads, we need to use the banana bond representation of double bond proposed by Linus Pauling. This also means that, to construct a correct bead valence bond model of a double bond, we have to use a bead with a curved channel with an angle about 71 degree. I don't think one can get commercial beads which have channels with this particular angle.

But to illustrate the idea of banana bond, here I try to make a styrofoam ball/rubber band model of ethylene by carefully puncturing a channel with approximately this angle (see the styrofoam ball in the center). The resulting styrofoam model of ethylene looks just great!

It is straightforward to construct valence sphere model of acetylene with five styrofoam balls. Three of these balls represent triple bond and the remaining two balls represent single C-H bonds. Using the elementary geometry, one can show that the angle of the curved channel for the ball representing triple bond is about 38 degrees.

Styrofoam ball/rubber band model

Bead models can be viewed as a kind of valence sphere models (or tangent sphere models 價球模型或是切球模型), in which beads represent electron pairs. Similar idea using styrofoam balls and rubber band has been exploited in the 60s by L. Carrol King, a chemistry professor in the Northwestern university. Here is the first styrofoam ball/rubber band model of methane that I made.

Many people use this model to illustrate the valence sphere electron repulsion theory (VSEPR) for molecules with four valence electron pairs. We can easily see that the energy of the model in the square planar configuration is higher than that in the tetrahedral configuration. But one has to be careful in the interpretation because the energy difference in the total energy of these two configurations is from the elastic energy of the rubber band, instead of the repulsion energy among four hard spheres.