Chapter 18 · Organic Chemistry
18.3Carbon: A Versatile Atom
8 min · two checks
Predict
How many bonds does carbon almost always form in organic molecules?
The idea
- Draw carbon with four bonds.
- Explain catenation.
Carbon has four valence electrons and completes an octet by forming four covalent bonds. The geometry of four single bonds is tetrahedral, about 109.5°. A double bond uses two of those valences and the geometry around that carbon becomes trigonal planar. A triple bond leaves the carbon linear. If your drawing gives carbon five bonds or two, the drawing is wrong.
Carbon–carbon bonds are strong enough that chains and rings persist. Silicon, just below carbon, also has four valence electrons but Si–Si bonds are weaker and silicon chains are not the backbone of a whole chemistry. Add hydrogen to satisfy unused valences and you have a hydrocarbon. Add other atoms and you have the functional groups that organize the rest of the chapter.
Keep these
- Carbon forms four bonds.
- Single: tetrahedral. Double: planar at that carbon. Triple: linear.
- Stable C–C bonds allow long chains, called catenation.