Carbon is phenomenally important to life as we understand it. The ability to form bonds with up to four different atoms gives carbon an incredible chemical diversity, and allows for carbon to make long chains and aromatic compounds. The ability to make long chains and aromatic compounds accounts for the formation of nucleic acids, proteins, and lipids (macromolecules that are absolutely essential to life). Binding properties of carbon also relate to the structure and orientation of biological compounds, which are important aspects of organic chemistry.

In its ground state carbon has four valence electrons, two its full s subshell and two in a partially filled p subshell. Normally, this would indicate that carbon forms two bonds, since only two of the electrons are in orbitals that are not already paired. Carbon, however, is able to form hybrid orbitals by combining the three p orbitals and one s orbital to form four identical sp³ orbitals, each containing one electron. This means that carbon can form four bonds, allowing it to achieve a stable octet.

For biology, the important note is that carbon can make four bonds. Organic chemistry is the study of carbon and how these bonds function to create organic and biological materials.

Carbon has four valance electrons, allowing it to form a wide range of bonds with other atoms.

When carbon bonds to four separate substituents, it forms a tetrahedral structure. Because of its ability to hybridize orbitals, carbon can also bond to three substituents by forming a double bond, or to two substituents via two double bonds or the combination of a single bond and a triple bond. This variability in molecular bonding and shape allows carbon to exist in numerous compounds, exhibiting a number of different properties and functions.

Carbon is incapable of forming a quadruple bond, and it is not magnetic. Though carbon has a relatively low atomic mass, one would expect hydrogen to be the most relevant element if low mass was the most pertinent property of carbon. Carbon can form ionic bonds (generally with metals), but is most commonly found in organic molecules where it forms covalent bonds.

Life is "carbon-based" or predominantly carbon because it can form stable bonds with itself, but also with a variety of other types of elements. Electronegativity increases from left to right on the periodic table, but also from bottom to top. While carbon is relatively high and right on the periodic chart, there are still elements like oxygen or fluorine (the most electronegative) that have a great pull for electrons. While carbon makes up a lot of the universe, it pales in comparison to hydrogen which is the most common element (three fourths of the mass of our universe). Therefore ratios do not matter. The polar and nonpolar nature of molecules are important for the functions of life (like membranes), but were it not for the bonding of carbon to itself, the nonpolar molecules would not be able to form. Thus, its bonding versatility is the main reason for life being carbon based.

The chemical properties of an element are, in a large part, determined by the number of bonds that element can form with other elements. Silicon, like carbon, can form four bonds with other elements, and thus is the most similar. This can easily be seen on a periodic table as elements with similar properties are grouped together in the same column. Note that these similarities arise from having the same number of valence electrons.