capable of weighing masses of the
order 10
–6 to 10
–9 kg.
microcrystal test See crystal test.
microscopic Designating a size
scale comparable to the subatomic
particles, atoms, and molecules.
Microscopic objects and systems are
described by *quantum mechanics.
Compare macroscopic; mesoscopic.
microscopic reversibility The
principle that in a reversible reaction
the mechanism in one direction is
the exact reverse of the mechanism
in the other direction. See also detailed balance.
microwaves Electromagnetic
waves with wavelengths in the range
10
–3 to 0.03 m.
microwave spectroscopy A sensitive technique for chemical analysis
and the determination of molecular
structure (bond lengths, bond angles,
and dipole moments), and also relative atomic masses. It is based on the
principle that microwave radiation
(see microwaves) causes changes in
the rotational energy levels of molecules and absorption consequently
occurs at characteristic frequencies.
In a microwave spectrometer a microwave source, usually a klystron
valve, produces a beam that is passed
through a gaseous sample. The beam
then impinges on the detector, usually a crystal detector, and the signal
(wavelength against intensity) is displayed, either as a printed plot or on
an oscilloscope. As microwaves are
absorbed by air the instrument is
evacuated.
migration 1. The movement of a
group, atom, or double bond from
one part of a molecule to another.
2. The movement of ions under the
inÛuence of an electric Üeld.
milk of magnesia See magnesium
hydroxide.
milk sugar See lactose.
Miller indices A set of three numbers that characterize a face of a crystal. The French mineralogist René
Just Haüy (1743–1822) proposed the
law of rational intercepts, which
states that there is always a set of
axes, known as crystal axes, that allows a crystal face to be characterized in terms of intercepts of the face
with these axes. The reciprocals of
these intercepts are small rational
numbers. When the fractions are
cleared there is a set of three integers. These integers are known as the
Miller indices of the crystal face after
the British mineralogist William Hallowes Miller (1810–80), who pointed
out that crystal faces could be characterized by these indices.
If a plane is parallel to one of the
crystal axes then its intercept is at
inÜnity and hence its reciprocal is 0.
If a face cuts a crystal axis on the
negative side of the origin then the
intercept, and hence its reciprocal,
i.e. the Miller index for that axis, are
negative. This is indicated by a bar
over the Miller index. For example,
the Miller indices for the eight faces
of an octahedron are (III), (I
_
II), (II
_
I),
(III
_
), (I
_
I
_
I), (II
_
I
_
), (I
_
II
_
) and (I
_
I
_
I
_
).
milli- Symbol m. A preÜx used in
the metric system to denote one
thousandth. For example, 0.001 volt
= 1 millivolt (mV).
Millon’s reagent A solution of
mercury(II) nitrate and nitrous acid
used to test for proteins. The sample
is added to the reagent and heated
for two minutes at 95°C; the formation of a red precipitate indicates the
presence of protein in the sample.
The reagent is named after French
chemist Auguste Millon (1812–67).
mineral A naturally occurring substance that has a characteristic chemical composition and, in general, a
355
mineral
m
www.AzShimi.ir www.AzShimi.com
order 10
–6 to 10
–9 kg.
microcrystal test See crystal test.
microscopic Designating a size
scale comparable to the subatomic
particles, atoms, and molecules.
Microscopic objects and systems are
described by *quantum mechanics.
Compare macroscopic; mesoscopic.
microscopic reversibility The
principle that in a reversible reaction
the mechanism in one direction is
the exact reverse of the mechanism
in the other direction. See also detailed balance.
microwaves Electromagnetic
waves with wavelengths in the range
10
–3 to 0.03 m.
microwave spectroscopy A sensitive technique for chemical analysis
and the determination of molecular
structure (bond lengths, bond angles,
and dipole moments), and also relative atomic masses. It is based on the
principle that microwave radiation
(see microwaves) causes changes in
the rotational energy levels of molecules and absorption consequently
occurs at characteristic frequencies.
In a microwave spectrometer a microwave source, usually a klystron
valve, produces a beam that is passed
through a gaseous sample. The beam
then impinges on the detector, usually a crystal detector, and the signal
(wavelength against intensity) is displayed, either as a printed plot or on
an oscilloscope. As microwaves are
absorbed by air the instrument is
evacuated.
migration 1. The movement of a
group, atom, or double bond from
one part of a molecule to another.
2. The movement of ions under the
inÛuence of an electric Üeld.
milk of magnesia See magnesium
hydroxide.
milk sugar See lactose.
Miller indices A set of three numbers that characterize a face of a crystal. The French mineralogist René
Just Haüy (1743–1822) proposed the
law of rational intercepts, which
states that there is always a set of
axes, known as crystal axes, that allows a crystal face to be characterized in terms of intercepts of the face
with these axes. The reciprocals of
these intercepts are small rational
numbers. When the fractions are
cleared there is a set of three integers. These integers are known as the
Miller indices of the crystal face after
the British mineralogist William Hallowes Miller (1810–80), who pointed
out that crystal faces could be characterized by these indices.
If a plane is parallel to one of the
crystal axes then its intercept is at
inÜnity and hence its reciprocal is 0.
If a face cuts a crystal axis on the
negative side of the origin then the
intercept, and hence its reciprocal,
i.e. the Miller index for that axis, are
negative. This is indicated by a bar
over the Miller index. For example,
the Miller indices for the eight faces
of an octahedron are (III), (I
_
II), (II
_
I),
(III
_
), (I
_
I
_
I), (II
_
I
_
), (I
_
II
_
) and (I
_
I
_
I
_
).
milli- Symbol m. A preÜx used in
the metric system to denote one
thousandth. For example, 0.001 volt
= 1 millivolt (mV).
Millon’s reagent A solution of
mercury(II) nitrate and nitrous acid
used to test for proteins. The sample
is added to the reagent and heated
for two minutes at 95°C; the formation of a red precipitate indicates the
presence of protein in the sample.
The reagent is named after French
chemist Auguste Millon (1812–67).
mineral A naturally occurring substance that has a characteristic chemical composition and, in general, a
355
mineral
m
www.AzShimi.ir www.AzShimi.com