Radium chloride (RaCl
2) is a salt of
radium
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather t ...
and
chlorine
Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
, and the first
radium
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather t ...
compound
Compound may refer to:
Architecture and built environments
* Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall
** Compound (fortification), a version of the above fortified with defensive struct ...
isolated in a pure state.
Marie Curie
Marie Salomea Skłodowska–Curie ( , , ; born Maria Salomea Skłodowska, ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first ...
and
André-Louis Debierne
André-Louis Debierne (; 14 July 1874 – 31 August 1949) was a French chemist. He is often considered the discoverer of the element actinium, though H. W. Kirby disputes this and awards credit instead to German chemist Friedrich Oskar Giesel.
De ...
used it in their original separation of radium from
barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
. The first preparation of radium metal was by the
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of a solution of this salt using a mercury cathode.
Preparation
Radium chloride crystallises from solution as the di
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
. It may be dehydrated by heating to 100 °C in air for one hour followed by hours at 520 °C under
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
. If the presence of other anions is suspected, the dehydration may be effectuated by fusion under
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
.
Radium chloride can also be prepared by heating radium bromide in a flow of dry
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
gas, or can be isolated from uranium and thorium ores by treating radium sulfate with sodium carbonate, leaving radium carbonate and then reacting the radium carbonate in hydrochloric acid.
Properties
Radium chloride is a colorless-white salt with a blue-green
luminescence
Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light".
It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a cryst ...
, especially when heated. Its color gradually changes to yellow with aging, whereas contamination by barium may impart a rose tint.
[ It is less soluble in water than other ]alkaline earth metal
The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are al ...
chlorides – at 25 °C its solubility is 245 g/L whereas that of barium chloride
Barium chloride is an inorganic compound with the formula Ba Cl2. It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is white, highly toxic, and imparts a yellow-green coloration to a flame. ...
is 307 g/L, and the difference is even larger in hydrochloric acid solutions. This property is used in the first stages of the separation of radium from barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
by fractional crystallization Fractional crystallization may refer to:
* Fractional crystallization (chemistry), a process to separate different solutes from a solution
* Fractional crystallization (geology)
Fractional crystallization, or crystal fractionation, is one of the ...
.[ Radium chloride is only sparingly soluble in ]azeotropic
An azeotrope () or a constant heating point mixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple distillation.Moore, Walter J. ''Physical Chemistry'', 3rd e Prentice-Hall 1962, pp. 140–142 This ...
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
and virtually insoluble in concentrated hydrochloric acid.
Gaseous radium chloride exists as RaCl2 molecules, as with other alkaline earth metal halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...
s. The gas shows strong absorptions in the visible spectrum at 676.3 nm and 649.8 nm (red): the dissociation energy
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical s ...
of the radium–chlorine bond is estimated as 2.9 eV, and its length
Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Interna ...
as 292 pm.
Contrary to diamagnetic barium chloride, radium chloride is weakly paramagnetic
Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...
with a magnetic susceptibility
In electromagnetism, the magnetic susceptibility (Latin: , "receptive"; denoted ) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the ap ...
of 1.05. It also differs from barium chloride by the flame color, which is red as opposed to green for barium chloride.[
]
Uses
Radium chloride is still used for the initial stages of the separation of radium from barium during the extraction of radium from pitchblende
Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes th ...
. The large quantities of material involved (to extract a gram of pure radium metal, about 7 tonnes of pitchblende is required) favour this less costly (but less efficient) method over those based on radium bromide
Radium bromide is the bromide salt of radium, with the formula RaBr2. It is produced during the process of separating radium from uranium ore. This inorganic compound was discovered by Pierre and Marie Curie in 1898, and the discovery sparked a hug ...
or radium chromate
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather t ...
(used for the later stages of the separation).
It was also used in medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...
to produce radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
gas which in turn was used as a brachytheraputic cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
treatment.
Radium-223 dichloride ( USP, radium chloride Ra 223), tradename Xofigo (formerly Alpharadin), is an alpha-emitting radiopharmaceutical
Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is ...
. Bayer
Bayer AG (, commonly pronounced ; ) is a German multinational corporation, multinational pharmaceutical and biotechnology company and one of the largest pharmaceutical companies in the world. Headquartered in Leverkusen, Bayer's areas of busi ...
received FDA approval for this drug to treat prostate cancer
Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that sur ...
osteoblastic bone metastases in May 2013. Radium-223 chloride is one of the most potent ((antineoplastic drugs)) known. One dose (50 kBq/kg) in an adult is about 60 nanograms; this amount is 1/1000 the weight of an eyelash (75 micrograms).
References
Bibliography
*Kirby, H. W. and Salutsky, Murrell L. (1964
The Radiochemistry of Radium
Subcommittee on Radiochemistry, National Academy of Sciences
Sources
*''Gmelins Handbuch der anorganischen Chemie (8. Aufl.)'', Berlin:Verlag Chemie, 1928, pp. 60–61.
*''Gmelin Handbuch der anorganischen Chemie (8. Aufl. 2. Erg.-Bd.)'', Berlin:Springer, 1977, pp. 362–64.
{{Chlorides
Chlorides
Alkaline earth metal halides
Radium compounds