white metallic element belonging to
*group 1 (formerly IA) of the periodic
table; a.n. 37; r.a.m. 85.47; r.d. 1.53;
m.p. 38.89°C; b.p. 688°C. It is found
in a number of minerals (e.g. lepidolite) and in certain brines. The metal
is obtained by electrolysis of molten
rubidium chloride. The naturally occurring isotope rubidium–87 is radioactive (see rubidium–strontium
dating). The metal is highly reactive,
with properties similar to those of
other group 1 elements, igniting
spontaneously in air. It was discovered spectroscopically by Robert Bunsen and Gustav Kirchhoff in 1861.
A
• Information from the WebElements site
rubidium–strontium dating A
method of dating geological specimens based on the decay of the radioisotope rubidium–87 into the
stable isotope strontium–87. Natural
rubidium contains 27.85% of rubidium–87, which has a half-life of 4.7 ×
10
10 years. The ratio
87 Rb/
87 Sr in a
specimen gives an estimate of its age
(up to several thousand million
years).
ruby The transparent red variety of
the mineral *corundum, the colour
being due to the presence of traces of
chromium. It is a valuable gemstone,
more precious than diamonds. The
Ünest rubies are obtained from
Mogok in Burma, where they occur
in metamorphic limestones; Sri
Lanka and Thailand are the only
other important sources. Rubies have
been produced synthetically by the
Verneuil Ûame-fusion process. Industrial rubies are used in lasers,
watches, and other precision instruments.
Russell–Saunders coupling (L–S
coupling) A type of coupling in systems involving many *fermions.
These systems include electrons in
atoms and nucleons in nuclei, in
which the energies associated with
electrostatic repulsion are much
greater than the energies associated
with *spin–orbit coupling. *Multiplets of many-electron atoms with a
low atomic number are characterized
by Russell–Saunders coupling. It is
named after the US physicists Henry
Norris Russell (1877–1957) and Frederick Saunders (1875–1963) who postulated this type of coupling to
explain the spectra of many-electron
atoms with low atomic number in
1925. The multiplets of heavy atoms
and nuclei are better described by *jj coupling or intermediate coupling,
i.e. a coupling in which the energies
of electrostatic repulsion and
spin–orbit coupling are similar in
size.
rusting Corrosion of iron (or steel)
to form a hydrated iron(III) oxide
Fe 2 O 3 .xH 2 O. Rusting occurs only in
the presence of both water and oxygen. It is an electrochemical process
in which different parts of the iron
surface act as electrodes in a cell reaction. At the anode, iron atoms dissolve as Fe
2+ ions:
Fe(s) → Fe
2+ (aq) + 2e
At the cathode, hydroxide ions are
formed:
O 2 (aq) + 2H 2 O(l) + 4e → 4OH
–
(aq)
The Fe(OH) 2 in solution is oxidized to
Fe 2 O 3 . Rusting is accelerated by impurities in the iron and by the presence of acids or other electrolytes in
the water.
ruthenium Symbol Ru. A hard
white metallic *transition element;
a.n. 44; r.a.m. 101.07; r.d. 12.3; m.p.
2310°C; b.p. 3900°C. It is found associated with platinum and is used as a
catalyst and in certain platinum alloys. Chemically, it dissolves in fused
alkalis but is not attacked by acids. It
reacts with oxygen and halogens at
467
ruthenium
r
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*group 1 (formerly IA) of the periodic
table; a.n. 37; r.a.m. 85.47; r.d. 1.53;
m.p. 38.89°C; b.p. 688°C. It is found
in a number of minerals (e.g. lepidolite) and in certain brines. The metal
is obtained by electrolysis of molten
rubidium chloride. The naturally occurring isotope rubidium–87 is radioactive (see rubidium–strontium
dating). The metal is highly reactive,
with properties similar to those of
other group 1 elements, igniting
spontaneously in air. It was discovered spectroscopically by Robert Bunsen and Gustav Kirchhoff in 1861.
A
• Information from the WebElements site
rubidium–strontium dating A
method of dating geological specimens based on the decay of the radioisotope rubidium–87 into the
stable isotope strontium–87. Natural
rubidium contains 27.85% of rubidium–87, which has a half-life of 4.7 ×
10
10 years. The ratio
87 Rb/
87 Sr in a
specimen gives an estimate of its age
(up to several thousand million
years).
ruby The transparent red variety of
the mineral *corundum, the colour
being due to the presence of traces of
chromium. It is a valuable gemstone,
more precious than diamonds. The
Ünest rubies are obtained from
Mogok in Burma, where they occur
in metamorphic limestones; Sri
Lanka and Thailand are the only
other important sources. Rubies have
been produced synthetically by the
Verneuil Ûame-fusion process. Industrial rubies are used in lasers,
watches, and other precision instruments.
Russell–Saunders coupling (L–S
coupling) A type of coupling in systems involving many *fermions.
These systems include electrons in
atoms and nucleons in nuclei, in
which the energies associated with
electrostatic repulsion are much
greater than the energies associated
with *spin–orbit coupling. *Multiplets of many-electron atoms with a
low atomic number are characterized
by Russell–Saunders coupling. It is
named after the US physicists Henry
Norris Russell (1877–1957) and Frederick Saunders (1875–1963) who postulated this type of coupling to
explain the spectra of many-electron
atoms with low atomic number in
1925. The multiplets of heavy atoms
and nuclei are better described by *jj coupling or intermediate coupling,
i.e. a coupling in which the energies
of electrostatic repulsion and
spin–orbit coupling are similar in
size.
rusting Corrosion of iron (or steel)
to form a hydrated iron(III) oxide
Fe 2 O 3 .xH 2 O. Rusting occurs only in
the presence of both water and oxygen. It is an electrochemical process
in which different parts of the iron
surface act as electrodes in a cell reaction. At the anode, iron atoms dissolve as Fe
2+ ions:
Fe(s) → Fe
2+ (aq) + 2e
At the cathode, hydroxide ions are
formed:
O 2 (aq) + 2H 2 O(l) + 4e → 4OH
–
(aq)
The Fe(OH) 2 in solution is oxidized to
Fe 2 O 3 . Rusting is accelerated by impurities in the iron and by the presence of acids or other electrolytes in
the water.
ruthenium Symbol Ru. A hard
white metallic *transition element;
a.n. 44; r.a.m. 101.07; r.d. 12.3; m.p.
2310°C; b.p. 3900°C. It is found associated with platinum and is used as a
catalyst and in certain platinum alloys. Chemically, it dissolves in fused
alkalis but is not attacked by acids. It
reacts with oxygen and halogens at
467
ruthenium
r
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