Radium chloride, RaCl
2, was the first
radiumRadium is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black. Radium is an alkaline earth metal that is found in trace amounts in uranium ores. It is extremely radioactive...
compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
to be prepared in a pure state and was the basis of
Marie CurieMarie Skłodowska Curie was a physicist and chemist of Polish upbringing and, subsequently, French citizenship...
's original separation of radium from
bariumBarium is a chemical element. It has the symbol Ba, atomic number 56, and is the fifth element in Group 2. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts...
. The first preparation of radium metal was by the
electrolysisIn chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic...
of a solution of radium chloride using a mercury cathode.
Radium chloride crystallises from solution as the di
hydrateHydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
. It may be dehydrated by heating to 100 °C in air for one hour followed by 5½ hours at 520 °C under
argonArgon is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is present in the Earth's atmosphere at 0.94%. Terrestrially, it is the most abundant and most frequently used of the noble gases...
.
Radium chloride, RaCl
2, was the first
radiumRadium is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black. Radium is an alkaline earth metal that is found in trace amounts in uranium ores. It is extremely radioactive...
compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
to be prepared in a pure state and was the basis of
Marie CurieMarie Skłodowska Curie was a physicist and chemist of Polish upbringing and, subsequently, French citizenship...
's original separation of radium from
bariumBarium is a chemical element. It has the symbol Ba, atomic number 56, and is the fifth element in Group 2. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts...
. The first preparation of radium metal was by the
electrolysisIn chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic...
of a solution of radium chloride using a mercury cathode.
Preparation
Radium chloride crystallises from solution as the di
hydrateHydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
. It may be dehydrated by heating to 100 °C in air for one hour followed by 5½ hours at 520 °C under
argonArgon is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is present in the Earth's atmosphere at 0.94%. Terrestrially, it is the most abundant and most frequently used of the noble gases...
. If the presence of other anions is suspected, the dehydration may be effectuated by fusion under
hydrogen chlorideThe compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
.
Properties
Radium chloride is a white solid with a blue-green
luminescenceLuminescence is light that usually occurs at low temperatures, and is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light generated by high...
, especially when heated. It is less soluble in water than other
alkaline earth metalThe alkaline earth metals are a series of elements comprising Group 2 of the periodic table: beryllium , magnesium , calcium , strontium , barium and radium . This specific group in the periodic table owes its name to their oxides that simply give basic alkaline solutions...
chlorides, a fact which is used in the first stages of the separation of radium from
bariumBarium is a chemical element. It has the symbol Ba, atomic number 56, and is the fifth element in Group 2. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts...
by
fractional crystallizationIn chemistry, fractional crystallization is a method of refining substances based on differences in solubility. If two or more substances are dissolved in a solvent, they will crystallize out of solution at different rates. Crystallization can be induced by changes in concentration, temperature...
. It is only sparingly soluble in
azeotropicAn azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation...
hydrochloric acidHydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong mineral acid and has major industrial uses. It is found naturally in gastric acid....
and virtually insoluble in concentrated hydrochloric acid.
Gaseous radium chloride exists as RaCl
2 molecules, as with other alkaline earth metal
halideA halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. Many salts are halides...
s. The gas shows strong absorptions in the visible spectrum at 676.3
nmA nanometre is a unit of length in the metric system, equal to one billionth of a meter....
and 649.8 nm (red): the
dissociation energyIn chemistry, bond dissociation energy, D0 or BDE, is one measure of the bond strength in a chemical bond. It is defined as the standard enthalpy change when a bond is cleaved by homolysis, with reactants and products of the homolysis reaction at 0 K...
of the radium–chlorine bond is estimated as 2.9
eVIn physics, the electron volt is a unit of energy. By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electrostatic potential difference of one volt...
, and its
lengthIn molecular geometry, bond length or bond distance is the average distance between nuclei of two bonded atoms in a molecule.- Explanation :...
as 292
pmA picometre is a unit of length in the metric system, equal to one trillionth or one billionth , i.e. of a meter, which is the current SI base unit of length...
.
Uses
Radium chloride is still used for the initial stages of the separation of radium from barium during the extraction of radium from pitchblende. The large quantities of material involved (
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s of ore for milligrams of radium) favour this less costly (but less efficient) method over those based on
radium bromideRadium bromide is the bromide salt of radium, with the formula RaBr2. It is used in separating radium from uranium ore....
or radium chromate (used for the later stages of the separation).
It is also used in
medicineMedicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
to produce
radonRadon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of radium. It is one of the heaviest substances that remains a gas under normal conditions and is considered to be a health...
gas which in turn is used as a
cancerCancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
treatment.
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.