the rate is given by
R = k[A]
x [B]
y
where k is the *rate constant. The
principle was introduced by C. M.
Guldberg and P. Waage in 1863. It is
strictly correct only for ideal gases. In
real cases *activities can be used. See
also equilibrium constant.
mass concentration See concentration.
massicot See lead(ii) oxide.
mass number See nucleon number.
mass spectroscopy A technique
used to determine relative atomic
masses and the relative abundance of
isotopes, and for chemical analysis
and the study of ion reactions. In a
mass spectrometer a sample (usually
gaseous) is ionized and the positive
ions produced are accelerated into a
high-vacuum region containing electric and magnetic Üelds. These Üelds
deÛect and focus the ions onto a detector. The Üelds can be varied in a
controlled way so that ions of different types can impinge on the detector. A mass spectrum is thus obtained
consisting of a series of peaks of variable intensity to which mass/charge
(m/e) values can be assigned. The original ions are usually produced by
electron impact, although ion impact, photoionization, Üeld ionization, *electrospray ionization, and
*MALDI are also used. For organic
molecules, the mass spectrum consists of a series of peaks, one corresponding to the parent ion and the
others to fragment ions produced by
the ionization process. Different molecules can be identiÜed by their characteristic pattern of lines. Analysis of
mixtures can be done by gas chromatography–mass spectroscopy (see
gas chromatography). Other types
of mass spectrometer exist. In a
quadrupole mass spectrometer the
ions pass along a region surrounded
by four parallel rods. Variable voltages applied to the rods produce an
oscillating electric Üeld. Varying the
frequency of osillation allows different ions to pass through to a detector. In a time-of-Ûight mass
spectrometer the ions are accelerated
by an electric Üeld and then enter a
drift tube through which they pass to
a detector. Different types of ion are
distinguished by their time of Ûight
in the drift tube.
masurium A former name for
*technetium.
matrix (pl. matrices) 1. (in chemistry) A continuous solid phase in
which particles (atoms, ions, etc.) are
embedded. Unstable species, such as
free radicals, can be trapped in an
unreactive substrate, such as solid
argon, and studied by spectroscopy.
The species under investigation are
separated by the matrix, hence the
term matrix isolation for this technique. 2. (in geology) The Ünegrained material of rock in which the
coarser-grained material is embedded. 3. (in mathematics) A set of
quantities in a rectangular array,
used in certain mathematical operations. The array is usually enclosed in
large parentheses or in square brackets.
matrix mechanics A formulation
of *quantum mechanics using matrices (see matrix) to represent states
and operators. Matrix mechanics was
the Ürst formulation of quantum mechanics to be stated (by Werner
Heisenberg in 1925) and was developed by Heisenberg and Max Born
(1882–1970) and the German physicist Pascual Jordan (1902–80). It was
shown by Erwin Schrödinger in 1926
to be equivalent to the *wave mechanics formulation of quantum mechanics.
mass concentration
344
m
www.AzShimi.ir www.AzShimi.com
R = k[A]
x [B]
y
where k is the *rate constant. The
principle was introduced by C. M.
Guldberg and P. Waage in 1863. It is
strictly correct only for ideal gases. In
real cases *activities can be used. See
also equilibrium constant.
mass concentration See concentration.
massicot See lead(ii) oxide.
mass number See nucleon number.
mass spectroscopy A technique
used to determine relative atomic
masses and the relative abundance of
isotopes, and for chemical analysis
and the study of ion reactions. In a
mass spectrometer a sample (usually
gaseous) is ionized and the positive
ions produced are accelerated into a
high-vacuum region containing electric and magnetic Üelds. These Üelds
deÛect and focus the ions onto a detector. The Üelds can be varied in a
controlled way so that ions of different types can impinge on the detector. A mass spectrum is thus obtained
consisting of a series of peaks of variable intensity to which mass/charge
(m/e) values can be assigned. The original ions are usually produced by
electron impact, although ion impact, photoionization, Üeld ionization, *electrospray ionization, and
*MALDI are also used. For organic
molecules, the mass spectrum consists of a series of peaks, one corresponding to the parent ion and the
others to fragment ions produced by
the ionization process. Different molecules can be identiÜed by their characteristic pattern of lines. Analysis of
mixtures can be done by gas chromatography–mass spectroscopy (see
gas chromatography). Other types
of mass spectrometer exist. In a
quadrupole mass spectrometer the
ions pass along a region surrounded
by four parallel rods. Variable voltages applied to the rods produce an
oscillating electric Üeld. Varying the
frequency of osillation allows different ions to pass through to a detector. In a time-of-Ûight mass
spectrometer the ions are accelerated
by an electric Üeld and then enter a
drift tube through which they pass to
a detector. Different types of ion are
distinguished by their time of Ûight
in the drift tube.
masurium A former name for
*technetium.
matrix (pl. matrices) 1. (in chemistry) A continuous solid phase in
which particles (atoms, ions, etc.) are
embedded. Unstable species, such as
free radicals, can be trapped in an
unreactive substrate, such as solid
argon, and studied by spectroscopy.
The species under investigation are
separated by the matrix, hence the
term matrix isolation for this technique. 2. (in geology) The Ünegrained material of rock in which the
coarser-grained material is embedded. 3. (in mathematics) A set of
quantities in a rectangular array,
used in certain mathematical operations. The array is usually enclosed in
large parentheses or in square brackets.
matrix mechanics A formulation
of *quantum mechanics using matrices (see matrix) to represent states
and operators. Matrix mechanics was
the Ürst formulation of quantum mechanics to be stated (by Werner
Heisenberg in 1925) and was developed by Heisenberg and Max Born
(1882–1970) and the German physicist Pascual Jordan (1902–80). It was
shown by Erwin Schrödinger in 1926
to be equivalent to the *wave mechanics formulation of quantum mechanics.
mass concentration
344
m
www.AzShimi.ir www.AzShimi.com