Dictionary of Chemistry [6th Ed.]

angle between ± 90 °and 180°. An-
other distinction is between clinal
arrangements (value between 30°
and 150°or –30°and –150°) and peri-
planararrangements (value between
0 and ± 30 °or ± 150 °and 180°). Com-
bining the two gives four ranges of
torsion angle in an arrangement:
synperiplanar(sp) 0°to ± 30 °;
synclinal(sc) 30°to 90°or –30°to
–90°;
anticlinal(ac) 90°to 150°or –90°to
–150°;
antiperiplanar(ap) ± 150 °to 180°.
The antiperiplanar conformation is
also called a transconformation; the
synperiplanar conformation corre-
sponds to a cisconformation. The
synclinal conformation is also called
a gaucheor skewconformation.

total-radiation pyrometer See py-
rometry.

tourmalineA group of minerals
composed of complex cyclosilicates
containing boron with the general
formula NaR 3 2+Al 6 B 3 Si 6 O 27 (H,F) 4 ,
where R = Fe2+, Mg, or (Al + Li). The
crystals are trigonal, elongated, and
variably coloured, the two ends of
the crystals often having different
colours. Tourmaline is used as a gem-
stone and because of its double re-
fraction and piezoelectric properties
is also used in polarizers and some
pressure gauges.

town gasAny manufactured gas
supplied as a fuel gas to domestic
and industrial users. Examples in-
clude coal gas, substitute natural
gas (SNG), and *natural gas itself.
Most town gases are based on hydro-
gen or methane, although coal gas
also contains up to 8% carbon
monoxide.

trace element See essential el-
ement.

tracing(radioactive tracing)See la-
belling.

transSee isomerism; torsion

angle.

transactinide elementsElements

with an atomic number greater than

103, i.e. elements above lawrencium

in the *periodic table. So far, el-

ements up to 116 have been de-

tected. Because of the highly

radioactive and transient nature of

these elements, there has been much

dispute about priority of discovery

and, consequently, naming of the el-

ements. The International Union of

Pure and Applied Chemistry (IUPAC)

introduced a set of systematic tempo-

rary names based on afÜxes, as

shown in the table.

531 transactinide elements

t

Affix Number Symbol

nil 0 n

un 1 u

bi 2 b

tri 3 t

quad 4 q

pent 5 p

hex 6 h

sept 7 s

oct 8 o

enn 9 e

All these element names end in

-ium. So, for example, element 109 in

this system is called un + nil + enn +

ium, i.e. unnilennium, and given the

symbol u+n+e, i.e. Une.

One long-standing dispute was

about the element 104 (ruther-

fordium), which has also been called

kurchatovium (Ku). There have also

been disputes between IUPAC and

the American Chemical Union about

element names.

In 1994 IUPAC suggested the fol-

lowing list:

mendelevium (Md, 101)

nobelium (No, 102)

lawrencium (Lr, 103)

dubnium (Db, 104)