Lewis base A molecular entity able to provide a pair
of electrons and thus capable of COORDINATIONto a
LEWIS ACID, thereby producing a LEWIS ADDUCT.
Lewis formula (electron dot or Lewis structure)
Molecular structure in which the valence electrons are
shown as dots placed between the bonded atoms, with
one pair of dots representing two electrons or one (sin-
gle) COVALENT BOND, for example
A double bond is represented by two pairs of dots,
etc. Dots representing nonbonded outer-shell electrons
are placed adjacent to the atoms with which they are
associated, but not between the atoms. Formal charges
(e.g. +, –, 2+, etc.) are attached to atoms to indicate the
difference between the positive nuclear charge (atomic
number) and the total number of electrons (including
those in the inner shells) on the formal basis that bond-
ing electrons are shared equally between atoms they
join. (Bonding pairs of electrons are usually denoted by
lines, representing covalent bonds, as in LINE
FORMULAe.)
Libby, Willard Frank(1908–1980) AmericanPhysi-
cal chemist Willard Frank Libby was born in Grand
Valley, Colorado, on December 17, 1908, to Ora
Edward Libby and Eva May (née Rivers). After attend-
ing grammar and high schools near Sebastopol, Cali-
fornia (1913–26), he attended the University of
California at Berkeley from 1927 to 1933, taking his
bachelor’s and Ph.D. degrees in 1931 and 1933, respec-
tively.
In 1933 he became an instructor in the department
of chemistry at California University (Berkeley), even-
tually becoming associate professor of chemistry. He
was awarded a Guggenheim Memorial Foundation Fel-
lowship in 1941, but he went to Columbia University
to work on the Manhattan Project, on leave from the
Department of Chemistry, California University, until
1945.
After the war Libby became professor of chemistry
in the department of chemistry and Institute for
Nuclear Studies (Enrico Fermi Institute for Nuclear
Studies) of the University of Chicago. In 1954 he was
appointed by President Eisenhower to the U.S. Atomic
Energy Commission, staying until 1959, when he
became professor of chemistry in the University of Cali-
fornia at Los Angeles. He became founding director of
the UCLA Institute of Geophysics and Planetary
Physics in 1962.
Libby developed carbon dating, a method of using
carbon-14 for age determination in archaeology, geol-
ogy, geophysics, and other branches of science. He was
awarded the Nobel Prize in chemistry in 1960 “for his
method to use carbon-14 for age determination in
archaeology, geology, geophysics, and other branches
of science.”
He also received the Research Corporation Award
for 1951 for the radiocarbon dating technique; the
Chandler Medal of Columbia University for outstand-
ing achievement in the field of chemistry (1954); the
American Chemical Society Award for Nuclear Appli-
cations in Chemistry (1956); the Elliott Cresson
Medal of the Franklin Institute (1957); the American
Chemical Society’s Willard Gibbs Medal Award
(1958); the Albert Einstein Medal Award (1959); and
the Day Medal of the Geological Society of America
(1961).
Libby published Radiocarbon Dating (1952),
authored numerous scientific articles, and was a mem-
ber of the editorial board of the Proceedings of the
National Academy of Sciencesand of Science.
He died on September 8, 1980, in Los Angeles,
California.lifetime(mean lifetime τ) The lifetime of a CHEMI-
CAL SPECIESthat decays in a first-order process is the
time needed for a concentration of this species to
decrease to 1/e of its original value. Statistically, it rep-
resents the mean life expectancy of an excited species.
In a reacting system in which the decrease in concentra-
tion of a particular chemical species is governed by a
first-order RATE LAW, it is equal to the reciprocal of the
sum of the (pseudo)unimolecular rate constants of all
processes that cause the decay. When the term is used
for processes that are not first order, the lifetime
depends on the initial concentration of the species, or164 Lewis base