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Carbon is tetravalent, meaning it can form four covalent bonds with other atoms such as hydrogen, nitrogen, and oxygen. This flexibility allows carbon to create diverse molecular structures that form the basis of all living organisms. Because carbon's valence electrons are stable, it rarely becomes an ion, making it an extraordinarily reliable structural component of biological molecules.

Structural isomers are molecules with the same chemical formula but different structural arrangements. Hexane and isohexane both have the formula C6H14, but hexane is a linear chain while isohexane has a branch point on the second carbon atom. These different arrangements create molecules with distinct properties despite containing identical numbers of atoms.

As carbon chains increase in length, structural modifications become possible, including ring structures, double bonds at different positions, and branching side chains. For example, hexane forms a linear chain, while hexenes contain double bonds, and cyclohexene forms a ring structure. These variations allow the same number of carbon and hydrogen atoms to create molecules with vastly different properties.

Functional groups bonded to the carbon skeleton confer unique properties to biological molecules. Groups such as amino (–NH2) or methyl (–CH3) alter the structural and chemical properties of molecules. The properties of functional groups influence many fields, including synthetic drug design, making them critical to understanding molecular behavior.

Hydrocarbons are molecules containing only hydrogen and carbon atoms. Hydrogen atoms readily bond to carbon atoms, forming long chains or branches protruding at various points. The simplest hydrocarbon, methane, has a single carbon atom bonded to four hydrogen atoms, while longer carbon chains create increasingly complex molecules.

Changing the number of bonds between carbon atoms changes the molecule's properties. A fatty acid with a long hydrocarbon tail containing one or more double bonds behaves differently than a fatty acid with no double bonds. These structural variations in bonding create molecules with distinct chemical and physical characteristics.

Enantiomers are a type of isomer that are mirror images of each other. While all enantiomers share the same chemical formula and connectivity, their three-dimensional spatial arrangements differ. This distinction is important in biological systems, where enantiomers can have dramatically different effects despite their identical molecular composition.