Tetravalence

Tetravalence is the property of an atom or ion having valence four, meaning it can form up to four covalent bonds with other atoms. Carbon is the quintessential tetravalent element, because its four valence electrons allow it to form four covalent bonds and create a vast range of structures. Other elements in the same group, such as silicon, germanium, tin, and lead, can also display tetravalent behavior in their compounds, typically in a +4 oxidation state.

In bonding terms, tetravalence is often linked to sp3 hybridization, which yields a tetrahedral arrangement of four substituents around the central atom and bond angles close to 109.5 degrees. Molecular geometry can deviate from the ideal tetrahedron due to multiple bonds, ring strain, or steric effects. It is also possible for an atom to achieve four valence connections through a mix of single and multiple bonds; for example, methane has four single bonds, ethene has one double bond and two singles, and carbon dioxide has two double bonds—each carbon forming four valence connections.

Tetravalence is a cornerstone of organic chemistry because carbon can bond with many different atoms and with itself, enabling long chains, branching, rings, and aromatic systems. This capability underpins the diversity of organic compounds, biopolymers, and many materials. The concept also applies in inorganic chemistry to elements that form four covalent bonds or adopt a +4 oxidation state in compounds, such as titanium(IV) or tin(IV) species.