2007 Schools Wikipedia Selection. Related subjects: Chemical elements
|Name, Symbol, Number||radium, Ra, 88|
|Chemical series||alkaline earth metals|
|Group, Period, Block||2, 7, s|
|Appearance||silvery white metallic|
|Atomic mass||(226) g/mol|
|Electron configuration||[Rn] 7s2|
|Electrons per shell||2, 8, 18, 32, 18, 8, 2|
|Density (near r.t.)||5.5 g·cm−3|
|Melting point||973 K
(700 ° C, 1292 ° F)
|Boiling point||2010 K
(1737 ° C, 3159 ° F)
|Heat of fusion||8.5 kJ·mol−1|
|Heat of vaporization||113 kJ·mol−1|
|Crystal structure||cubic body centered|
(strongly basic oxide)
|Electronegativity||0.9 (Pauling scale)|
|Ionization energies||1st: 509.3 kJ/mol|
|2nd: 979.0 kJ/mol|
|Atomic radius||215 pm|
|Electrical resistivity||(20 °C) 1 µΩ·m|
|Thermal conductivity||(300 K) 18.6 W·m−1·K−1|
|CAS registry number||7440-14-4|
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. Its most stable isotope, 226Ra, has a half-life of 1602 years and decays into radon gas.
The heaviest of the alkaline earth metals, radium is intensely radioactive and resembles barium in its chemical behaviour. This metal is found in minute quantities in the uranium ore pitchblende, and various other uranium minerals. Radium preparations are remarkable for maintaining themselves at a higher temperature than their surroundings, and for their radiations, which are of three kinds: alpha particles, beta particles, and gamma rays. Radium also produces neutrons when mixed with beryllium.
When freshly prepared, pure radium metal is brilliant white, but blackens when exposed to air (probably due to nitride formation). Radium is luminescent (giving a faint blue colour), reacts violently with water to form radium hydroxide and is slightly more volatile than barium.
Some of the practical uses of radium are derived from its radiative properties. More recently discovered radioisotopes, such as cobalt-60 and caesium-137, are replacing radium in even these limited uses because several of these are much more powerful and others are safer to handle.
- Formerly used in self-luminous paints for watches, aircraft switches, clocks, and instrument dials. More than 100 former watch dial painters who used their lips to shape the paintbrush died from the radiation. Soon afterward, the adverse effects of radioactivity became widely known. Radium was still used in dials as late as the 1950's. Objects painted with this paint may still be dangerous, and must be handled properly. Although tritium's beta radiation is potentially dangerous if ingested, it has replaced radium in these applications.
- When mixed with beryllium it is a neutron source for physics experiments.
- Radium (usually in the form of radium chloride) is used in medicine to produce radon gas which in turn is used as a cancer treatment.
- Radium was also put in many foods for taste and a preservative, but also exposed many people to radiation
- Radium-223 is currently under investigation for use in medicine as cancer treatment of bone metastasis.
- One unit for radioactivity, the non- SI curie, is based on the radioactivity of radium-226 (see Radioactivity).
- At the turn of the 20th century radium was a popular additive in products like toothpaste, hair creams, and even food items due to its supposed curative powers. Such products soon fell out of vogue, and were prohibited by authorities in many countries, after it was discovered they could have real and serious adverse health effects. (See for instance Radithor.)
- Spas featuring radium-rich water are still occasionally touted as beneficial, such as those in Misasa, Tottori, Japan.
Radium (Latin radius, ray) was discovered by Maria Skłodowska-Curie and her husband Pierre in 1898 in pitchblende/ uraninite from North Bohemia (area around Jáchymov). While studying pitchblende the Curies removed uranium from it and found that the remaining material was still radioactive. They then separated out a radioactive mixture mostly consisting of barium which gave a brilliant red flame colour and spectral lines which had never been documented before. In 1902 radium was isolated into its pure metal by Curie and Andre Debierne through the electrolysis of a pure radium chloride solution by using a mercury cathode and distilling in an atmosphere of hydrogen gas.
Historically the decay products of radium were known as Radium A, B, C, etc. These are now known to be isotopes of other elements as follows:
- Radium emanation - radon-222
- Radium A - polonium-218
- Radium B - lead-214
- Radium C - bismuth-214
- Radium C1 - polonium-214
- Radium C2 - thallium-210
- Radium D - lead-210
- Radium E - bismuth-210
- Radium F - polonium 210
- Radium A - polonium-218
On February 4, 1936 radium E became the first radioactive element to be made synthetically.
During the 1930s it was found that workers exposure to radium by handling luminescent paints caused serious health effects which included sores, anaemia and bone cancer. This use of radium was stopped soon afterward. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow, and can mutate bone cells. Handling of radium has since been blamed for Marie Curie's premature death.
Radium is a decay product of uranium and is therefore found in all uranium-bearing ores. Radium was originally acquired from pitchblende ore from Joachimsthal, Bohemia (One metric ton of pitchblende yields 0.0001 grams of radium). Carnotite sands in Colorado provide some of the element, but richer ores are found in the Democratic Republic of the Congo, the Great Lakes area of Canada and can also be extracted from uranium processing waste. Large uranium deposits are located in Ontario, New Mexico, Utah, Virginia, Australia, and in other places.
Its compounds colour flames crimson carmine (rich red or crimson colour with a shade of purple) and give a characteristic spectrum. Due to its geologically short half life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.
- radium fluoride (Ra F2)
- radium chloride (RaCl2)
- radium bromide (RaBr2)
- radium iodide (RaI2)
- radium oxide (RaO)
Radium has 25 different known isotopes, four of which are found in nature, with 226Ra being the most common. 223Ra, 224Ra, 226Ra and 228Ra are all generated in the decay of either U or Th. 226Ra is a product of 238U decay, and is the longest-lived isotope of radium with a half-life of 1602 years; next longest is 228Ra, a product of 232Th breakdown, with a half-life of 6.7 years.
Radium is over one million times more radioactive than the same mass of uranium. Its decay occurs in at least seven stages; the successive main products have been studied and were called radium emanation or exradio (this is radon), radium A (polonium), radium B (lead), radium C (bismuth), etc. The radon is a heavy gas and the later products are solids. These products are themselves radioactive elements, each with an atomic weight a little lower than its predecessor.
Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight with lead being a final product of disintegration.
The SI unit of radioactivity is the becquerel (Bq), equal to one disintegration per second. The curie is a non-SI unit defined as that amount of radioactivity which has the same disintegration rate as 1 gram of Ra-226 (3.7 x 1010 disintegrations per second, or 37 GBq).
Radium is highly radioactive and its decay product, radon gas, is also radioactive. Since radium is chemically similar to calcium, it has the potential to cause great harm by replacing it in bones. Inhalation, injection, ingestion or body exposure to radium can cause cancer and other disorders. Stored radium should be ventilated to prevent accumulation of radon.
Emitted energy from the decay of radium ionizes gases, affects photographic plates, causes sores on the skin, and produces many other detrimental effects.