metry it is a spherical top. If it has a
threefold or higher axis of symmetry
it is a symmetric top. If it does not
have a threefold or higher axis of
symmetry it is an asymmetric top.
All linear molecules (and hence all
diatomic molecules) are linear
rotors.
In reality, molecules are not rigid
rotors because of the centrifugal
forces associated with the rotation.
The effect of such forces can be
taken into account by adding a cor-
rection term to the rigid rotor model.monatomic moleculeA ‘mol-
ecule’ consisting of only one atom
(e.g. Ar or He), distinguished from di-
atomic and polyatomic molecules.
Mond process A method of obtain-
ing pure nickel by heating the im-
pure metal in a stream of carbon
monoxide at 50–60°C. Volatile nickel
carbonyl (Ni(CO) 4 ) is formed, and this
can be decomposed at higher tem-
peratures (180°C) to give pure nickel.
The method was invented by the Ger-
man–British chemist Ludwig Mond
(1839–1909).Monel metalAn alloy of nickel
(60–70%), copper (25–35%), and small
quantities of iron, manganese, sili-
con, and carbon. It is used to make
acid-resisting equipment in the
chemical industry.
monobasic acidAn *acid that has
only one acidic hydrogen atom in its
molecules. Hydrochloric (HCl) and ni-
tric (HNO 3 ) acids are common exam-
ples.monoclinicSee crystal system.
monoethanolamineSee
ethanolamine.
monoglycerideSee glyceride.monohydrateA crystalline com-
pound having one mole of water per
mole of compound.monomerA molecule (or com-
pound) that joins with others in
forming a dimer, trimer, or polymer.monosaccharide(simple sugar)A
carbohydrate that cannot be split
into smaller units by the action of di-
lute acids. Monosaccharides are
classiÜed according to the number of
carbon atoms they possess: trioses
have three carbon atoms; tetroses,
four; pentoses,Üve; hexoses, six; etc.
Each of these is further divided into
aldosesand ketoses, depending on
whether the molecule contains an
aldehyde group (–CHO) or a ketone
group (–CO–). For example glucose,
having six carbon atoms and an alde-
hyde group, is an aldohexose
whereas fructose is a ketohexose.
These aldehyde and ketone groups
confer reducing properties on mono-
saccharides: they can be oxidized to
yield sugar acids. They also react
with phosphoric acid to produce
phosphate esters (e.g. in *ATP),
which are important in cell metabo-
lism. Monosaccharides can exist as ei-
ther straight-chain or ring-shaped
molecules. They also exhibit *optical
activity, giving rise to both dextro-
rotatory and laevorotatory forms.monosodium glutamate (MSG)A
white solid, C 8 H 8 NNaO 4 .H 2 O, used
extensively as aÛavour enhancer, es-
pecially in convenience foods. It is a
salt of glutamic acid (an *amino
acid), from which it is prepared. It
can cause an allergic reaction in
some susceptible people who con-
sume it.
monotropy See allotropy.monovalent(univalent)Having a
valency of one.Monte Carlo methodA numeri-
cal method for solving mathematical
and physical problems that involves
the random sampling of numbers.
Applications of Monte Carlo methodsmonatomic molecule 360m