grey metallic *transition element;
a.n. 73; r.a.m. 180.948; r.d. 16.63;
m.p. 2996°C; b.p. 5427°C. It is found
with niobium in the ore columbite–
tantalite (Fe,Mn)(Ta,Nb) 2 O 6. It is ex-
tracted by dissolving in hydroÛuoric
acid, separating the tantalum and
niobiumÛuorides to give K 2 TaF 7 , and
reduction of this with sodium. The
element contains the stable isotope
tantalum–181 and the long-lived
radioactive isotope tantalum–180
(0.012%; half-life > 107 years). There
are several other short-lived isotopes.
The element is used in certain alloys
and in electronic components. Tanta-
lum parts are also used in surgery be-
cause of the unreactive nature of the
metal (e.g. in pins to join bones).
Chemically, the metal forms a pas-
sive oxide layer in air. It forms com-
plexes in the +2, +3, +4, and +5
oxidation states. Tantalum was
identiÜed in 1802 by Anders Ekeberg
(1767–1813) andÜrst isolated in 1820
by *Berzelius.
A- Information from the WebElements site
tarAny of various black semisolid
mixtures of hydrocarbons and free
carbon, produced by destructive dis-
tillation of *coal or by *petroleum
reÜning.target moleculeSee retrosyn-
thetic analysis.tar sandSee oil sand.tartaric acidA crystalline natu-
rally occurring carboxylic acid,
(CHOH) 2 (COOH) 2 ; r.d. 1.8; m.p.
171–174°C. It can be obtained from
tartar (potassium hydrogen tartrate)
deposits from wine vats, and is used
in baking powders and as a food-
stuffs additive. The compound is
optically active (see optical activity).
The systematic name is 2,3-
dihydroxybutanedioic acid.tartrateA salt or ester of *tartaric
acid.tartrazineA food additive (E102)
that gives foods a yellow colour. Tar-
trazine can cause a toxic response in
the immune system and is banned in
some countries.TATP See triacetone triperoxide.
tautomerismA type of *iso-
merism in which the two isomers
(tautomers) are in equilibrium. See
keto–enol tautomerism.
TCA cycleSee krebs cycle.technetiumSymbol Tc. A radio-
active metallic *transition element;
a.n. 43; m.p. 2172°C; b.p. 4877°C. The
element can be detected in certain
stars and is present in theÜssion
products of uranium. It wasÜrst
made by Carlo Perrier and Emilio
Segré (1905–89) by bombarding
molybdenum with deuterons to give
technetium–97. The most stable iso-
tope is technetium–99 (half-life 2.6 ×
106 years); this is used to some extent
in labelling for medical diagnosis.
There are sixteen known isotopes.
Chemically, the metal has properties
intermediate between manganese
and rhenium.
A- Information from the WebElements site
TeÛonTradename for a form of
*polytetraÛuoroethene.Teichmann test See haematin
test.tele-substitutionA type of substi-
tution reaction in which the entering
group takes a position on an atom
that is more than one atom away
from the atom to which the leaving
group is attached. See also cine-
substitution.
telluridesBinary compounds of tel-
lurium with other more electroposi-tar 518t