Chemistry of the Radioactive Elements(1912–14), Mat-
ter and Energy(1912), Science and Life(1920), The
Interpretation of the Atom(1932), The Story of Atomic
Energy(1949), and Atomic Transmutation(1953).
Soddy died on September 22, 1956, at Brighton,
Sussex.
sodium-potassium pump An ACTIVE TRANSPORT
mechanism of cell membranes to regulate pressure
between the inside and outside of the cell and to pump
potassium ions into the cell and keep sodium out,
thereby preventing water retention and swelling within
the cell. The sodium-potassium pump also maintains
the electrical charge within each cell. ATPis used as the
energy source for the pump.
soft acid SeeHARD ACID.
soft base SeeHARD BASE.
soft drug A compound that is degraded in vivo to
predictable nontoxic and inactive METABOLITEs after
having achieved its therapeutic role.
sol A colloid (HETEROGENEOUS MIXTUREof tiny par-
ticles suspended in another material) with solid parti-
cles suspended in a liquid, e.g., protoplasm.
solar energy Heat and light radiated from the Sun.
solar radiation Electromagnetic radiation (light
energy in the form of photons) emitted by the Sun that
hits the Earth.
sol-gel process Sol-gel is a colloidal suspension of
silica particles that is gelled to form a solid. The sol-gel
process, created by Bell Labs, allows silica to be modi-
fied with a variety of dopants to produce novel kinds
of glass. The technique has been extended to the pro-
duction of other types of materials such as ceramics.
solid solution A HOMOGENEOUS MIXTUREof two or
more components. A main component and (normally) a
small amount of another component exist within the
crystal structure of the main component.solubility product constant Equilibrium constant
that applies to the solution of a slightly soluble ionic
compound added to water.solubility product principle The expression of the
solubility product constant for a slightly soluble com-
pound is the product of the concentrations of the con-
stituent ions, each raised to the power that corresponds
to the number of ions in one formula unit.solute Any dissolved substance in a solution.solution Any liquid mixture of two or more sub-
stances that is homogeneous.solvation Any stabilizing interaction of a solute (or
solute MOIETY) with the solvent, or a similar interac-
tion of solvent with groups of an insoluble material
(i.e., the ionic groups of an ion-exchange resin). Such
interactions generally involve electrostatic forces and
VAN DERWAALS FORCES, as well as chemically more
specific effects such as HYDROGEN BONDformation.
See alsoCYBOTACTIC REGION.solvatochromic relationship A LINEAR FREE-
ENERGY RELATIONSHIPbased on SOLVATOCHROMISM.
See alsoKAMLET-TAFT SOLVENT PARAMETERS.solvatochromism The (pronounced) change in posi-
tion and sometimes intensity of an electronic absorption
or emission band, accompanying a change in the polar-
ity of the medium. Negative (positive) solvatochromism
corresponds to a HYPSOCHROMIC (BATHOCHROMIC)
SHIFTwith increasing solvent POLARITY.
See alsoDIMROTH-REICHARDT ETPARAMETER; Z-
VALUE.250 sodium-potassium pump
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