tive elements. Compounds of tel-
lurium with nonmetals are covalent
(e.g. H 2 Te). Metal tellurides can be
made by direct combination of the el-
ements and are ionic (containing
Te2–) or nonstoichiometric interstitial
compounds (e.g. Pd 4 Te, PdTe 2 ).
telluriumSymbol Te. A silvery met-
alloid element belonging to group
16 (formerly VIB) of the periodic
table; a.n. 52; r.a.m. 127.60; r.d. 6.24
(crystalline); m.p. 449.5°C; b.p.
989.8°C. It occurs mainly as tel-
lurides in ores of gold, silver, copper,
and nickel and it is obtained as a by-
product in copper reÜning. There are
eight natural isotopes and nine radio-
active isotopes. The element is used
in semiconductors and small
amounts are added to certain steels.
Tellurium is also added in small
quantities to lead. Its chemistry is
similar to that of sulphur. It was dis-
covered by Franz Müller (1740–1825)
in 1782.
A
- Information from the WebElements site
temperature The property of a
body or region of space that deter-
mines whether or not there will be a
netÛow of heat into it or out of it
from a neighbouring body or region
and in which direction (if any) the
heat willÛow. If there is no heatÛow
the bodies or regions are said to be in
thermodynamic equilibrium and at
the same temperature. If there is a
Ûow of heat, the direction of theÛow
is from the body or region of higher
temperature. Broadly, there are two
methods of quantifying this prop-
erty. The empirical method is to take
two or more reproducible tempera-
ture-dependent events and assign
Üxed points on a scale of values to
these events. For example, the Cel-
sius temperature scale uses the freez-
ing point and boiling point of water
as the twoÜxed points, assigns the
values 0 and 100 to them, respec-
tively, and divides the scale between
them into 100 degrees. This method
is serviceable for many practical pur-
poses (see temperature scales), but
lacking a theoretical basis it is awk-
ward to use in many scientiÜc con-
texts. In the 19th century, Lord
*Kelvin proposed a thermodynamic
method to specify temperature,
based on the measurement of the
quantity of heatÛowing between
bodies at different temperatures.
This concept relies on an absolute
scale of temperature with an *ab-
solute zero of temperature, at which
no body can give up heat. He also
used Sadi Carnot’s concept of an
ideal frictionless perfectly efÜcient
heat engine (see carnot cycle). This
Carnot engine takes in a quantity of
heat q 1 at a temperature T, and ex-
hausts heat q 2 at T 2 , so that T 1 /T 2 =
q 1 /q 2. If T 2 has a valueÜxed by deÜni-
tion, a Carnot engine can be run be-
tween thisÜxed temperature and
any unknown temperature T 1 , en-
abling T 1 to be calculated by measur-
ing the values of q 1 and q 2. This
concept remains the basis for deÜn-
ing thermodynamic temperature,
quite independently of the nature of
the working substance. The unit in
which thermodynamic temperature
is expressed is the *kelvin. In prac-
tice thermodynamic temperatures
cannot be measured directly; they
are usually inferred from measure-
ments with a gas thermometer con-
taining a nearly ideal gas. This is
possible because another aspect of
thermodynamic temperature is its re-
lationship to the *internal energy of
a given amount of substance. This
can be shown most simply in the
case of an ideal monatomic gas, in
which the internal energy per mole
(U) is equal to the total kinetic energy
of translation of the atoms in one
mole of the gas (a monatomic gas has519 temperature
t