Radium compounds are compounds containing the element

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 (rathe ...

(Ra). Due to radium's radioactivity, not many compounds have been well characterized. Solid radium compounds are white as radium ions provide no specific coloring, but they gradually turn yellow and then dark over time due to self-

radiolysis Radiolysis is the dissociation of molecules by ionizing radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux. The radiation in this context is associated with ionizing radiation; radiolysis is ...

from radium's

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an a ...

.Kirby et al., p. 4 Insoluble radium compounds coprecipitate with all barium, most

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ...

, and most

lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

compounds.Kirby et al., p. 8

Oxides and hydroxides

Radium oxide (RaO) has not been characterized well past its existence, despite oxides being common compounds for the other alkaline earth metals. Radium

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water ...

(Ra(OH)₂) is the most readily soluble among the alkaline earth hydroxides and is a stronger base than its barium congener,

barium hydroxide Barium hydroxide is a chemical compound with the chemical formula Ba(OH)2. The monohydrate (''x'' = 1), known as baryta or baryta-water, is one of the principal compounds of barium. This white granular monohydrate is the usual commercial form. P ...

.Kirby et al., pp. 4–8 It is also more soluble than actinium hydroxide and thorium hydroxide: these three adjacent hydroxides may be separated by precipitating them with

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...

Halides

Radium fluoride Radium fluoride is an inorganic compound with a chemical formula of . This salt, like all radium compounds is highly radioactive. It can be coprecipitated with lanthanide fluorides. Radium fluoride has the same crystal form as calcium fluoride ...

(RaF₂) is a highly radioactive compound. It can be

coprecipitated In chemistry, coprecipitation (CPT) or co-precipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed. Analogously, in medicine, coprecipitation is specifically the precipitation of an unbound " ...

with

lanthanide The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and y ...

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ...

s. Radium fluoride has the same crystal form as

calcium fluoride Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities. ...

(

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

).R.C. Ropp. Encyclopedia of the Alkaline Earth Compounds. Elsevier B.V., 2013. pp 68-69. It can be prepared by the reaction of

metal and hydrogen fluoride gas: : Ra + 2 HF → RaF₂ + H₂

Radium chloride Radium chloride (RaCl2) is a salt of radium and chlorine, and the first radium compound isolated in a pure state. Marie Curie and André-Louis Debierne used it in their original separation of radium from barium. The first preparation of radium met ...

(RaCl₂) is a colorless, luminous compound. It becomes yellow after some time due to self-damage by the

alpha radiation Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atomi ...

given off by radium when it decays. Small amounts of barium impurities give the compound a rose color. It is soluble in water, though less so than

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. ...

, and its solubility decreases with increasing concentration of

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. It is a component of the gastric acid in the dig ...

. Crystallization from aqueous solution gives the dihydrate RaCl₂·2H₂O, isomorphous with its barium analog.

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 hu ...

(RaBr₂) is also a colorless, luminous compound. In water, it is more soluble than radium chloride. Like radium chloride, crystallization from aqueous solution gives the dihydrate RaBr₂·2H₂O, isomorphous with its barium analog. The ionizing radiation emitted by radium bromide excites

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

molecules in the air, making it glow. The

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be pro ...

s emitted by radium quickly gain two electrons to become neutral

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

, which builds up inside and weakens radium bromide crystals. This effect sometimes causes the crystals to break or even explode.

Other compounds

Radium nitrate (Ra(NO₃)₂) is a white compound that can be made by dissolving radium carbonate in

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...

. As the concentration of nitric acid increases, the solubility of radium nitrate decreases, an important property for the chemical purification of radium. Radium forms much the same insoluble salts as its lighter congener barium: it forms the insoluble

sulfate The sulfate or sulphate ion is a polyatomic ion, polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salt (chemistry), ...

(RaSO₄, the most insoluble known sulfate), chromate (RaCrO₄),

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...

(RaCO₃),

iodate An iodate is the polyatomic anion with the formula . It is the most common form of iodine in nature, as it comprises the major iodine-containing ores. Iodate salts are often colorless. They are the salts of iodic acid. Structure Iodate is pyra ...

(Ra(IO₃)₂),

tetrafluoroberyllate Tetrafluoroberyllate or orthofluoroberyllate is an anion containing beryllium and fluorine. The fluoroanion has a tetrahedral shape, with the four fluorine atoms surrounding a central beryllium atom. It has the same size and outer electron stru ...

(RaBeF₄), and nitrate (Ra(NO₃)₂). With the exception of the carbonate, all of these are less soluble in water than the corresponding barium salts, but they are all isostructural to their barium counterparts. Additionally, radium

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

, radium

oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...

, and radium

sulfite Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are wide ...

are probably also insoluble, as they coprecipitate with the corresponding insoluble barium salts.Kirby et al., pp. 8–9 The great insolubility of radium sulfate (at 20 °C, only 2.1 mg will dissolve in 1 kg of water) means that it is one of the less biologically dangerous radium compounds.Kirby et al., p. 12 The large ionic radius of Ra²⁺ (148 pm) results in weak complexation and poor extraction of radium from aqueous solutions when not at high pH.

References

{{Radium compounds Compounds Chemical compounds by element

Oxides and hydroxides

Halides

Other compounds

See also

References