A
• The original paper by Raman and
Krishnan
Ramsay, Sir William (1852–1916)
British chemist, born in Glasgow.
After working under Robert *Bunsen, he returned to Glasgow before
taking up professorships at Bristol
(1880–87) and London (1887–1912). In
the early 1890s he worked with Lord
*Rayleigh on the gases in air and in
1894 they discovered argon. In 1898,
with Morris Travers (1872–1961), he
discovered neon, krypton, and
xenon. Six years later he discovered
the last of the noble gases, radon. He
was awarded the Nobel Prize for
chemistry in 1904, the year in which
Rayleigh received the physics prize.
random alloy See disordered
solid.
random walk The problem of determining the distance from a starting position made by a walker, who
can either move forward (toward +x)
or backwards (toward –x) with the
choice being made randomly (e.g. by
tossing a coin). The progress of the
walker is characterized by the net
distance D N travelled in N steps. After
N steps the root mean square value
D rms , which is the average distance
away from the starting position, is
given by D rms = √N. Physical applications of the random walk include diffusion and the related problem of
Brownian motion as well as problems involving the structures of polymers and disordered solids.
Raney nickel A spongy form of
nickel made by the action of sodium
hydroxide on a nickel–aluminium
alloy. The sodium hydroxide dissolves the aluminium leaving a
highly active form of nickel with a
large surface area. The material is a
black pyrophoric powder saturated
with hydrogen. It is an extremely
Ramsay, Sir William
454
r
efÜcient catalyst, especially for hydrogenation reactions at room temperature. It was discovered in 1927
by the American chemist M. Raney
(1885–1966).
ranksite A mineral consisting of
a mixed sodium carbonate, sodium
sulphate, and potassium chloride,
2Na 2 CO 3 .9Na 2 SO 4 .KCl.
Raoult’s law The partial vapour
pressure of a solvent is proportional
to its mole fraction. If p is the vapour
pressure of the solvent (with a substance dissolved in it) and X the mole
fraction of solvent (number of moles
of solvent divided by total number of
moles) then p = p 0 X, where p 0 is the
vapour pressure of the pure solvent.
A solution that obeys Raoult’s law is
said to be an ideal solution. In general the law holds only for dilute solutions, although some mixtures of
liquids obey it over a whole range of
concentrations. Such solutions are
perfect solutions and occur when the
intermolecular forces between molecules of the pure substances are
similar to the forces between molecules of one and molecules of the
other. Deviations in Raoult’s law for
mixtures of liquids cause the formation of *azeotropes. The law was discovered by the French chemist
François Raoult (1830–1901).
A
• Raoult’s original paper
rapeseed methyl ester See biofuel.
rare-earth elements See lanthanoids.
rarefaction A reduction in the
pressure of a Ûuid and therefore of
its density.
rare gases See noble gases.
Raschig process An industrial
process for making chlorobenzene
www.AzShimi.ir www.AzShimi.com
• The original paper by Raman and
Krishnan
Ramsay, Sir William (1852–1916)
British chemist, born in Glasgow.
After working under Robert *Bunsen, he returned to Glasgow before
taking up professorships at Bristol
(1880–87) and London (1887–1912). In
the early 1890s he worked with Lord
*Rayleigh on the gases in air and in
1894 they discovered argon. In 1898,
with Morris Travers (1872–1961), he
discovered neon, krypton, and
xenon. Six years later he discovered
the last of the noble gases, radon. He
was awarded the Nobel Prize for
chemistry in 1904, the year in which
Rayleigh received the physics prize.
random alloy See disordered
solid.
random walk The problem of determining the distance from a starting position made by a walker, who
can either move forward (toward +x)
or backwards (toward –x) with the
choice being made randomly (e.g. by
tossing a coin). The progress of the
walker is characterized by the net
distance D N travelled in N steps. After
N steps the root mean square value
D rms , which is the average distance
away from the starting position, is
given by D rms = √N. Physical applications of the random walk include diffusion and the related problem of
Brownian motion as well as problems involving the structures of polymers and disordered solids.
Raney nickel A spongy form of
nickel made by the action of sodium
hydroxide on a nickel–aluminium
alloy. The sodium hydroxide dissolves the aluminium leaving a
highly active form of nickel with a
large surface area. The material is a
black pyrophoric powder saturated
with hydrogen. It is an extremely
Ramsay, Sir William
454
r
efÜcient catalyst, especially for hydrogenation reactions at room temperature. It was discovered in 1927
by the American chemist M. Raney
(1885–1966).
ranksite A mineral consisting of
a mixed sodium carbonate, sodium
sulphate, and potassium chloride,
2Na 2 CO 3 .9Na 2 SO 4 .KCl.
Raoult’s law The partial vapour
pressure of a solvent is proportional
to its mole fraction. If p is the vapour
pressure of the solvent (with a substance dissolved in it) and X the mole
fraction of solvent (number of moles
of solvent divided by total number of
moles) then p = p 0 X, where p 0 is the
vapour pressure of the pure solvent.
A solution that obeys Raoult’s law is
said to be an ideal solution. In general the law holds only for dilute solutions, although some mixtures of
liquids obey it over a whole range of
concentrations. Such solutions are
perfect solutions and occur when the
intermolecular forces between molecules of the pure substances are
similar to the forces between molecules of one and molecules of the
other. Deviations in Raoult’s law for
mixtures of liquids cause the formation of *azeotropes. The law was discovered by the French chemist
François Raoult (1830–1901).
A
• Raoult’s original paper
rapeseed methyl ester See biofuel.
rare-earth elements See lanthanoids.
rarefaction A reduction in the
pressure of a Ûuid and therefore of
its density.
rare gases See noble gases.
Raschig process An industrial
process for making chlorobenzene
www.AzShimi.ir www.AzShimi.com