And some elements, particularly carbon, can have oxidation states from #-IV# to #+IV#. On the other hand, #"catenation"# is simply chain formation. Carbon again has a marked ability to catenate, to form long #CH_2-CH_2-CH_2# chains. Along the chains, there can be regions of different electronegativity (i.e. #C=C# and #C-=C# bonds), and substitution by heteroatoms, #O#, #N#, #S#, #"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......
