82 | The History and Use of Our Earth’s Chemical Elements Properties
82 | The History and Use of Our Earth’s Chemical Elements Properties
Radium is the last element in group 2 and is very similar to the other alkali earth metals, which makes it the largest and heaviest element in the group. It particularly resembles barium, which is just above it in group 2 of the periodic table. Radium is a bright white radioactive luminescent alkali earth metal that turns black when exposed to air. Its melting point is
700°C, its boiling point is 1,140°C, and its density is approximately 5.0 g/cm 3 . Characteristics Radium is extremely radioactive. It glows in the dark with a faint bluish light. Radium’s
radioisotopes undergo a series of four decay processes; each decay process ends with a stable isotope of lead. Radium-223 decays to Pb-207; radium-224 and radium-228decay to Pb-208; radium-226 decays to Pb-206; and radium-225 decays to Pb-209. During the decay processes three types of radiation—alpha (α), beta (β), and gamma (γ)—are emitted.
In addition to being radioactive, radium is extremely chemically reactive and forms many compounds. These radium compounds are not only radioactive but also toxic and should be handled by experienced personnel.
AbundanceandSource Radium is the 85th most abundant element found in the Earth’s crust. Radium is found in
the uranium ores pitchblende and chalcolite, which are both very radioactive. Radium metal exists to the extent of only one part to every three million parts of the uranium ore (pitch- blende). Only about one gram of radium is found in every seven or eight tons of uranium ore. This scarcity seems to be the reason that only about five pounds of uranium are produced each year in the entire world. Uranium ores are found in the states of Utah, New Mexico, and Colorado in the United States and in Canada, the Czech Republic, Slovakia, Russia, Zaire, and France.
History The French chemist Marie Sklodowska Curie (1867–1934) and her husband, Pierre Curie
(1859–1906), a physicist and chemist, are credited with the discovery of the element radium at the end of the nineteenth century in 1898. Marie imported tons of pitchblende (uranium ore), and by using small amounts of the ore for each of many procedures, she was able to extract the uranium. She found that the remaining ore was still radioactive after the uranium was removed. Over a period of four years of hard work, she further refined the ores by dis- solving the residues in acids, filtering the remainder, and then crystallizing the results. At the end, she had produced just 1/10 of a gram of radium. They used a spectroscope to identify several radioactive elements, including thorium and barium. During the spectroanalysis of a refined specimen, they saw a new spectral line, which she named radium after the Latin word radius. The same technique was used to identify another new element. Madam Curie named polonium after her native country, Poland. Marie Curie was one of only four people to receive two Nobel Prizes. In 1903 she and Pierre Curie and Henri Becquerel were jointly awarded the Nobel Prize in Physics for the discovery of spontaneous radioactivity. In 1911 she was awarded her second prize, this one in chemistry, for the discovery of two new elements, radium and polonium. Pierre Curie developed several techniques for measuring the strength of radiation, including his experiments with piezoelectricity that enabled him to measure the effects of
Guide to the Elements | 83 radiation emitted by radioactive crystals. He determined that each gram of radium gives off
140 calories of heat per hour and that the element has a half-life of over 1,600 years. CommonUses
Radium’s most important use is as a source of radiation in industry, medicine, and labora- tories. The isotope radium-226, which is the most abundant of all the 25 isotopes and has a half-life of 1630 years, is the only useful form of the element. It is used in the medical treat- ment of malignant cancer growth. It kills cancer cells that have spread throughout the body.
Other uses are to produce phosphorescence and fluorescence in organic compounds and for scintillation screens on instruments used to detect radiation. Radium salts were used in the past to paint the dials of luminous clock faces that glow in the dark.
ExamplesofCompounds Radium, like the other alkali earth metals, readily combines with halogens such as chlorine
and bromine (which are electronegative). RaCl 2 and RaBr 2 are the forms in which radium is usually stored and shipped for a variety of uses. Radium bromide (RaBr 2 ) is a source of radiation for treating cancer and for research in the field of physics.
Radium chloride (RaCl 2 ) has the same use as radium bromide.
Radium hydroxide (RaOH) is the most soluble of all the hydroxides of the alkali earth met- als. It is formed when radium reacts with water (2Ra + 2H 2 O → 2RaOH + H 2 ↑). Radium sulfate (RaSO 4 ) is the most insoluble sulfate known in chemistry and is created
when radium combines with a sulfate ion (Ra + H 2 SO 4 → RaSO 4 +H 2 ↑).
Hazards Because radium energetically emits three types of radiation, it poses great danger to anyone
handling it. In addition, it is toxic. If it is ingested in even small amounts, it replaces bone tissue, which can result in radiation sickness and death.
The Curies were both exposed to radiation and were the first persons to suffer from radia- tion sickness, resulting in an early death for Marie. Pierre was killed in an accident with a horse and carriage. Marie’s notebooks are still radioactive.
One of the decay products of radium is the gas radon, which can seep up through the Earth’s crust into basements and “slab level” homes. Good ventilation assures that the radon does not accumulate to the extent that would be harmful.
At one time, women painted clock and watch dials with luminous radium paint that was
a mixture of radium salts and zinc sulfide. They would place the small brushes between their lips and tongue to make the bristles more pointed, in order to paint fine lines with the radium paint. Over the years, they developed cancers that resulted in badly eaten-away and disfigured lips and jaws. Once the danger was known, luminous radium paint was banned for this use. Today, promethium (Pm-147), with a half-life of 2.4 years, is used for this purpose.
Transition Elements: Metals to Nonmetals