Linus Pauling (1901–1994) stands as one of the 20th century’s most influential scientists, credited with revolutionizing chemistry by applying the new, abstract laws of quantum mechanics (Articles 53, 54) to the practical problem of chemical bonding and molecular structure. He is the only person to have been awarded two unshared Nobel Prizes (Chemistry in 1954 and Peace in 1962). His work established the fundamental principles governing how atoms combine to form molecules, laying the groundwork for modern chemistry and molecular biology.
In the 1930s, Pauling synthesized the work of physicists and chemists to create a coherent, intuitive, and predictive theory of chemical bonding. His magnum opus, The Nature of the Chemical Bond (1939), became one of the most cited books in science.
Hybridization: Pauling introduced the concept of orbital hybridization (e.g., $sp^3$ in methane). He showed that atomic orbitals, like the $s$ and $p$ orbitals, mix to form new, identical hybrid orbitals that point in specific directions in space, dictating the geometric shape of the molecule. This explained the tetrahedral shape of carbon compounds.
Resonance: He developed the theory of resonance, showing that the structure of certain molecules (like benzene, $\text{C}_6\text{H}_6$) cannot be accurately represented by a single chemical drawing but exists as an intermediate state between two or more contributing structures. This stabilized structure is represented by delocalized electrons.
Pauling defined the concept of electronegativity as the measure of an atom's ability to attract electrons toward itself in a chemical bond.
Pauling Scale: He created the first widely accepted electronegativity scale, assigning values to elements (e.g., Fluorine is 3.98, the highest).
Bond Prediction: He showed that the difference in electronegativity between two atoms determines the nature of the bond: small differences result in covalent bonds, intermediate differences result in polar covalent bonds, and large differences result in ionic bonds. This provided chemists with a simple, yet powerful, tool to predict the properties and behavior of virtually any compound.
Pauling later applied his knowledge of molecular structure and geometry to biology, becoming a founder of molecular biology (though he narrowly missed the discovery of the DNA structure, Article 59).
Alpha Helix and Beta Sheet: In 1951, Pauling and Robert Corey correctly determined the two most common secondary structures of proteins: the alpha helix (a corkscrew structure) and the beta-pleated sheet (a folded, sheet-like structure). He deduced these structures based purely on the geometry and stability of the constituent amino acids and their hydrogen bonds, proving that the precise shape of biological molecules is critical to their function.
In Conclusion: Linus Pauling was the architect who translated quantum theory into the practical language of chemistry. By developing the concepts of electronegativity, hybridization, and resonance, he provided the fundamental rules governing how atoms bond and how molecules are shaped. His work not only modernized chemistry but also laid the essential structural foundation for all subsequent discoveries in molecular biology and medicine.