1.7 Why Carbon Is Special

We can imagine a single bond as being like two tetrahedra touching two points together, while if they touch edges, that's similar to a double bond, and if they touch faces, that's like a triple bond. But we can't touch all four vertices together, so elements with a valence of 4 cannot be diatomic - there is no such thing as C₂. That's why carbon is not a gas.

Carbon is also particularly good at forming stable covalent bonds. Its heavier cousin silicon is also tetravalent, but silicon-silicon bonds are not nearly as stable as carbon-carbon bonds, and most other tetravalent elements are metals that don't prefer to form covalent bonds. Carbon is uniquely able to arrange itself into stable chains and rings of atoms.

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