multidecker sandwichSee sand-
wich compound.
multiple bondA bond between
two atoms that contains more than
one pair of electrons. Such bonds pri-
marily involve sigma bonding with
secondary contribution from pi bond-
ing (or, sometimes, delta bonding).
See orbital.
multiple proportions See chemi-
cal combination.
multiplet1.A spectral line formed
by more than two (see doublet)
closely spaced lines. 2.A group of el-
ementary particles that are identical
in all respects except that of electric
charge.
multiplicityA quantity used in
atomic spectra to describe the en-
ergy levels of many-electron atoms
characterized by Russell–Saunders
coupling given by 2S + 1, where S is
the total electron spin quantum
number. The multiplicity of an en-
ergy level is indicated by a left super-
script to the value of L, where L is the
resultant electron orbital angular
momentum of the individual elec-
tron orbital angular momenta l.
multipole interactionsInterac-
tions between arrays of point charges
(multipoles) associated with potential
energies that depend on distance.
Multipole interactions are an impor-
tant feature of intermolecular forces.
An n-pole is a set of n charges having
an n-pole moment but not a lower
moment. A monopoleis a single
charge and the monopole moment is
the charge. A dipoleconsists of two
opposite charges and thus has no
overall charge (and hence no mono-
pole moment). Higher multipoles are
the quadrupole and the octupole.
The interaction potential energy be-
tween multipoles falls off with dis-
tance increasingly rapidly as the
order of the multipoles increases. If a
2 m-pole interacts with a 2n-pole, the
interaction potential energy, V,
varies with distance r as V =
c/(rm+n–1), where c is a constant. The
rapid fall-off with distance, as the
order increases, is due to the set of
charges appearing to tend towards
neutrality (as seen from outside). The
multipole interactions with the
largest interactions are: ion–ion,
ion–dipole, dipole–dipole, and disper-
sion interactions.MumetalThe original trade name
for a ferromagnetic alloy, containing
78% nickel, 17% iron, and 5% copper,
that had a high permeability and a
low coercive force. More modern ver-
sions also contain chromium and
molybdenum. These alloys are used
in some transformer cores and for
shielding various devices from exter-
nal magneticÜelds.Muntz metalA form of *brass con-
taining 60% copper, 39% zinc, and
small amounts of lead and iron.
Stronger than alpha-brass, it is used
for hot forgings, brazing rods, and
large nuts and bolts. It is named after
G. F. Muntz (1794–1857).muscovite(white mica; potash
mica)A mineral form of potassium
aluminosilicate, K 2 Al 4 (Si 6 Al 2 )O 20 -
(OH,F) 4 ; one of the most important
members of the *mica group of min-
erals. It is chemically complex and
has a sheetlike crystal structure (see
intercalation compound). It is usu-
ally silvery-grey in colour, sometimes
tinted with green, brown, or pink.
Muscovite is a common constituent
of certain granites and pegmatites. It
is also common in metamorphic and
sedimentary rocks. It is widely used
in industry, for example in the man-
ufacture of electrical equipment and
as aÜller in rooÜng materials, wall-
papers, and paint.363 muscovite
m