came a professor at Cambridge Uni-
versity in 1884. He is best known for
his work on cathode rays, which led
to his discovery of the electron in
- He went on to study the con-
duction of electricity through gases,
and it is for this work that he was
awarded the Nobel Prize for physics
in 1906. His son, Sir George Paget
Thomson(1892–1975), discovered
*electron diffraction, for which he
shared the 1937 Nobel Prize for
physics with Clinton J. Davisson
(1881–1958), who independently
made the same discovery.
Thomson, Sir William See kelvin,
lord.
thoriaSee thorium.
thoriumSymbol Th. A grey radio-
active metallic element belonging to
the actinoids; a.n. 90; r.a.m.
232.038; r.d. 11.5–11.9 (17°C); m.p.
1740–1760°C; b.p. 4780–4800°C. It oc-
curs in monazite sand in Brazil,
India, and USA. The isotopes of tho-
rium have mass numbers from 223
to 234 inclusive; the most stable iso-
tope, thorium–232, has a half-life of
1.39 × 1010 years. It has an oxidation
state of (+4) and its chemistry resem-
bles that of the other actinoids. It can
be used as a nuclear fuel for breeder
reactors as thorium–232 captures
slow neutrons to breed uranium–233.
Thorium dioxide (thoria, ThO 2 ) is
used on gas mantles and in special
refractories. The element was discov-
ered by J. J. Berzelius in 1829.
A
- Information from the WebElements site
thorium seriesSee radioactive se-
ries.
three-body problem See many-
body problem.
threnardite A mineral form of
*sodium sulphate, Na 2 SO 4.
threonine See amino acid.
thuliumSymbol Tm. A soft grey
metallic element belonging to the
*lanthanoids; a.n. 69; r.a.m. 168.934;
r.d. 9.321 (20°C); m.p. 1545°C; b.p.
1947 °C. It occurs in apatite and xeno-
time. There is one natural isotope,
thulium–169, and seventeen artiÜcial
isotopes have been produced. There
are no uses for the element, which
was discovered by Per Cleve (1840–
1905) in 1879.
A- Information from the WebElements site
thymidineA nucleoside consisting
of one thymine molecule linked to a
d-doxyribose sugar molecule.thymineA *pyrimidine derivative
and one of the major component
bases of *nucleotides and the nucleic
acid *DNA.527 thymol
t
thymolA pungent-smelling colour-NNOO3 CHThymineOHO2 CH
OHNNHOO3 CHThymidine