Microchem
Microscale Chemistry Experimentation for Teachers

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27. C₂H₂ orbital model (sp hybridisation)
Ethyne is a hydrocarbon which can be easily prepared fom calcium carbide and water.
An orbital model of its molecule can be assembled using two black and two white beads (C, H atoms), 10 microbeads (bonding electrons), plastic tubing (p orbitals, pi bond) and copper wire.

Left Ethyne molecule model showing the sigma skeleton from the side:
* The four bonded atoms point away from each other forming a streight line (sigma skeleton).
* Each of the two C atoms has two sp hybrid orbitals represented by golden and white microbeads.
* They form 1 C-C sigma bond and 1 C-H sigma bond.
* Two C-C pi bonds are modelled by two plastic loops.

* Right: In the same model the green and yellow plastic loops can be better seen because the line points to the observer.
* The loops represent the 2 C-C pi bonds formed by the overlap of the two unhybridized p orbitals of each C atom.
* They are perpendicular to the sigma skeleton.
* It can be seen that one of the two pi bonds is oriented horizontally and the other one vertically.
1 C-C sigma bond and 2 C-C pi bonds form a tripple bond.

The molecule model of C₂H₂ resembles that of nitrogen:                      28. N₂ orbital model (sp hybridization)