# What do we mean by "quadrivalency" in reference to carbon chemistry?

Well $\text{quadrivalency}$ is a description of oxidation state.......
And some elements, particularly carbon, can have oxidation states from $- I V$ to $+ I V$. On the other hand, $\text{catenation}$ is simply chain formation. Carbon again has a marked ability to catenate, to form long $C {H}_{2} - C {H}_{2} - C {H}_{2}$ chains. Along the chains, there can be regions of different electronegativity (i.e. $C = C$ and $C \equiv C$ bonds), and substitution by heteroatoms, $O$, $N$, $S$, $\text{halogen}$, which atoms can sometimes be included in the chain. Grow the chain long enuff, and you might make a molecule complex enough to support a biochemistry; i.e. self-replicating molecules, and life......