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People Behind the Science

Linus Carl Pauling (1901–1994)

inus Pauling was a U.S. theoretical a higher electronegativity. In hydrogen
Lchemist and biologist whose achieve- chloride (HCl), for example, hydrogen
ments ranked among the most important of has an electronegativity of 2.1 and chlo-
any in twentieth-century science. His main rine of 3.5. The bonding electrons are
contribution was to the understanding of pulled toward the chlorine atom, giving it
molecular structure and chemical bonding. a small excess negative charge (and leav-
He was one of the very few people to have ing the hydrogen atom with a small excess
been awarded two Nobel Prizes: he received positive charge), polarizing the hydrogen-
the 1954 Nobel Prize for chemistry (for his chlorine bond.
work on intermolecular forces) and the Pauling’s ideas on chemical bonding
1962 Peace Prize. Throughout his career, are fundamental to modern theories of mo-
his work was noted for the appli cation of lecular structure. Much of this work was
intuition and inspiration, assisted by his consolidated in his book The Nature of the
phenomenal memory; he often carried over Chemical Bond, The Structure of Molecules
principles from one field of science and and Crystals (1939). In the 1940s, Pauling
applied them to another field. turned his attention to the chemistry of
Pauling was born in Portland, Oregon, living tissues and systems. He applied his
on February 28, 1901, the son of a phar- knowledge of molecular structure to the
macist. He began his scientific studies at complexity of life, principally to proteins
Oregon State Agricultural College, from in blood. With Robert Corey, he worked on
which he graduated in chemical engineer- the structures of amino acids and polypep-
ing in 1922. He then began his research tides. They proposed that many proteins
at the California Institute of Technology, have structures held together with hydro-
Pasadena, earning his Ph.D. in 1925. He gen bonds, giving them helical shapes. This
became a full professor at Pasadena in that once paired, these electrons cannot concept assisted Francis Crick and James
1931 and left there in 1936 to take up the take part in the formation of other bonds. Watson in their search for the structure of
post of director of the Gates and Crellin It was followed by the book Introduction to DNA, which they eventually resolved as a
Laboratories, which he held for the next Quantum Mechanics (1935), of which he double helix.
22 years. He also held appointments at was coauthor. He was a pioneer in the ap- In his researches on blood, Pauling
the University of California, San Diego, plication of quantum mechanical principles investigated immunology and sickle-cell
and Stanford University. His last appoint- to the structures of molecules. anemia. Later work confirmed his hunch
ment was as director of the Linus Pauling It was Pauling who introduced the that the disease is genetic and that normal
Institute of Science and Medicine at Menlo concept of hybrid orbitals in molecules to hemoglobin and the hemoglobin in abnor-
Park, California. explain the symmetry exhibited by carbon mal “sickle” cells differ in electrical charge.
In 1931, Pauling published a classic atoms in most of its compounds. Pauling Throughout the 1940s, he studied living
paper, “The Nature of the Chemical Bond,” also investigated electronegativity of at- materials; he also carried out research on
in which he used quantum mechanics oms and polarization in chemical bonds. anesthesia. At the end of this period, he
to explain that an electron-pair bond is He assigned electronegativities on a scale published two textbooks, General Chem-
formed by the interaction of two unpaired up to 4.0. A pair of electrons in a bond is istry (1948) and College Chemistry (1950),
electrons, one from each of two atoms, and pulled preferentially toward an atom with which became bestsellers.

Source: Modified from the Hutchinson Dictionary of Scientific Biography © Research Machines 2008. All rights reserved. Helicon Publishing is a division of Research Machines.

SUMMARY

Elements are basic substances that cannot be broken down into any- A chemical change produces new substances with new properties,
thing simpler, and an atom is the smallest unit of an element. Com- and the new materials are created by making or breaking chemical
pounds are combinations of two or more elements and can be broken bonds. The process of chemical change in which different chemi-
down into simpler substances. Compounds are formed when atoms are cal substances are created by forming or breaking chemical bonds is
held together by an attractive force called a chemical bond. A molecule called a chemical reaction. During a chemical reaction, different chem-
is the smallest unit of a compound, or a gaseous element, that can exist ical substances with greater or lesser amounts of internal potential en-
and still retain the characteristic properties of a substance. ergy are produced. Chemical energy is the change of internal potential

9-17 CHAPTER 9 Chemical Bonds 245