In chemistry, catenation is the chemical linking of atoms of the same element into chains or rings. It is similar to polymerization, except the monomer units are atoms of an element. The term comes from the Latin word catena, which means “chain.” Catenated chemical structures are known as catenae.
Of all the elements, carbon is best known for catenation, as it readily forms covalent bonds with itself. Examples of carbon catenates include propane (C3H8, a linear catenate), 2-methylbutane (C₅H₁₂, a branched catenate), a cyclohexane (C₆H₁₂, a cyclic catenate).
Elements Capable of Catenation
The bond energy of an element binding with itself determines its likelihood of forming catenates. Other factors include electronegativity, steric factors, the ability to form covalent bonds, and the molecular orbital n. Atoms with less diffuse valence orbitals form catenates, while heavier elements have a harder time because they bond using higher valence shell orbitals.
So, elements that form catenates tend to be lighter and either nonmetals or semimetals (metalloids). These include carbon, oxygen, nitrogen, silicon, boron, phosphorus, sulfur, germanium, arsenic, bismuth, the halogens (except possibly fluorine), and hydrogen. Triiodide is a good example of a halogen catenate. Native sulfur exists as the catenate S8, although it spontaneously changes form in response to temperature and other changes. Hydrogen bonding between water molecules (hydrogen catenates) form tetrahedra and rings, giving liquid water a structural organization.
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