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 extracted by dissolving in hydroÛuoric
acid, separating the tantalum and
niobium Ûuorides 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 >10
7 years). There
are several other short-lived isotopes.
The element is used in certain alloys
and in electronic components. Tantalum parts are also used in surgery because of the unreactive nature of the
metal (e.g. in pins to join bones).
Chemically, the metal forms a passive oxide layer in air. It forms complexes in the +2, +3, +4, and +5
oxidation states. Tantalum was
identiÜed in 1802 by Anders Ekeberg
(1767–1813) and Ürst isolated in 1820
by *Berzelius.
A
• Information from the WebElements site
tar Any of various black semisolid
mixtures of hydrocarbons and free
carbon, produced by destructive distillation of *coal or by *petroleum
reÜning.
target molecule See retrosynthetic analysis.
tar sand See oil sand.
tartaric acid A crystalline naturally 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 foodstuffs additive. The compound is
optically active (see optical activity).
The systematic name is 2,3dihydroxybutanedioic acid.
tartrate A salt or ester of *tartaric
acid.
tartrazine A food additive (E102)
that gives foods a yellow colour. Tartrazine can cause a toxic response in
the immune system and is banned in
some countries.
TATP See triacetone triperoxide.
tautomerism A type of *isomerism in which the two isomers
(tautomers) are in equilibrium. See
keto–enol tautomerism.
TCA cycle See krebs cycle.
technetium Symbol Tc. A radioactive 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 the Üssion
products of uranium. It was Ürst
made by Carlo Perrier and Emilio
Segré (1905–89) by bombarding
molybdenum with deuterons to give
technetium–97. The most stable isotope is technetium–99 (half-life 2.6 ×
10
6 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
TeÛon Tradename for a form of
*polytetraÛuoroethene.
Teichmann test See haematin
test.
tele-substitution A type of substitution 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 cinesubstitution.
tellurides Binary compounds of tellurium with other more electropositar
518
t
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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 extracted by dissolving in hydroÛuoric
acid, separating the tantalum and
niobium Ûuorides 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 >10
7 years). There
are several other short-lived isotopes.
The element is used in certain alloys
and in electronic components. Tantalum parts are also used in surgery because of the unreactive nature of the
metal (e.g. in pins to join bones).
Chemically, the metal forms a passive oxide layer in air. It forms complexes in the +2, +3, +4, and +5
oxidation states. Tantalum was
identiÜed in 1802 by Anders Ekeberg
(1767–1813) and Ürst isolated in 1820
by *Berzelius.
A
• Information from the WebElements site
tar Any of various black semisolid
mixtures of hydrocarbons and free
carbon, produced by destructive distillation of *coal or by *petroleum
reÜning.
target molecule See retrosynthetic analysis.
tar sand See oil sand.
tartaric acid A crystalline naturally 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 foodstuffs additive. The compound is
optically active (see optical activity).
The systematic name is 2,3dihydroxybutanedioic acid.
tartrate A salt or ester of *tartaric
acid.
tartrazine A food additive (E102)
that gives foods a yellow colour. Tartrazine can cause a toxic response in
the immune system and is banned in
some countries.
TATP See triacetone triperoxide.
tautomerism A type of *isomerism in which the two isomers
(tautomers) are in equilibrium. See
keto–enol tautomerism.
TCA cycle See krebs cycle.
technetium Symbol Tc. A radioactive 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 the Üssion
products of uranium. It was Ürst
made by Carlo Perrier and Emilio
Segré (1905–89) by bombarding
molybdenum with deuterons to give
technetium–97. The most stable isotope is technetium–99 (half-life 2.6 ×
10
6 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
TeÛon Tradename for a form of
*polytetraÛuoroethene.
Teichmann test See haematin
test.
tele-substitution A type of substitution 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 cinesubstitution.
tellurides Binary compounds of tellurium with other more electropositar
518
t
www.AzShimi.ir www.AzShimi.com