Dictionary of Chemistry [6th Ed.]

amalgamAn alloy of mercury with
one or more other metals. Most met-
als form amalgams (iron and plat-
inum are exceptions), which may be
liquid or solid. Some contain deÜnite
intermetallic compounds, such as
NaHg 2.

amatol A high explosive consisting
of a mixture of ammonium nitrate
and trinitrotoluene.

ambidentDescribing a chemical
species that has two alternative reac-
tive centres such that reaction at one
centre stops or inhibits reaction at
the other. An example is the *eno-
late ion in which electrophilic attack
can occur at either the oxygen atom
or at the beta-carbon atom.

ambidentateDescribing a ligand
that can coordinate at two different
sites. For example, the NO 2 molecule
can coordinate through the N atom
(the nitro ligand) or through an O
atom (the nitrido ligand). Complexes
that differ only in the way the ligand
coordinates display linkage isomerism.

ambo- A preÜx used to indicate that
a substance is present as a mixture
of racemic diastereoisomers in un-
speciÜed proportions. For example, if
l-alanine is reacted with dl-leucine,
the resulting dipeptide can be de-

scribed as l-alanyl-ambo-leucine, to

indicate the mixture.

americiumSymbol Am. A radio-

active metallic transuranic element

belonging to the *actinoids; a.n. 95;

mass number of most stable isotope

243 (half-life 7.95 × 103 years); r.d.

13.67 (20°C); m.p. 994 ± 4 °C; b.p.

2607 °C. Ten isotopes are known. The

element was discovered by G. T.

Seaborg and associates in 1945, who

obtained it by bombarding ura-

nium–238 with alpha particles.

A

• Information from the WebElements site

amethystThe purple variety of the

mineral *quartz. It is found chieÛy in

Brazil, the Urals (Soviet Union), Ari-

zona (USA), and Uruguay. The colour

is due to impurities, especially iron

oxide. It is used as a gemstone.

amides1.Organic compounds con-

taining the group –CO.NH 2 (the

amide group). Compounds contain-

ing this group are primary amides.

Secondaryand tertiary amides can

also exist, in which the hydrogen

atoms on the nitrogen are replaced

by one or two other organic groups

respectively. Simple examples of pri-

mary amides are ethanamide,

CH 3 CONH 2 , and propanamide,

C 2 H 5 CONH 2. They are made by heat-

27 amides

a

H

N

H

H

3 CH

N

H

H

3 CH

N

CH 3

H

3 CH

N

CH 3

CH 3

ammonia

primary amine

(methylamine)

secondary amine

(dimethylamine)

tertiary amine

(trimethylamine)

amino group

imino group

Amines