Radium

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88 francium ← radium → actinium
Ba
↑
Ra
↓
Ubn
Periodic Table - Extended Periodic Table
General
Name, Symbol, Number radium, Ra, 88
Chemical series alkaline earth metals
Group, Period, Block 2, 7, s
Appearance silvery white metallic
Standard atomic weight (226)  g·mol−1
Electron configuration [Rn] 7s2
Electrons per shell 2, 8, 18, 32, 18, 8, 2
Physical properties
Phase solid
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
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 819 906 1037 1209 1446 1799
Atomic properties
Crystal structure cubic body centered
Oxidation states 2
(strongly basic oxide)
Electronegativity 0.9 (scale Pauling)
Ionization energies 1st: 509.3 kJ/mol
2nd: 979.0 kJ/mol
Atomic radius 215  pm
Miscellaneous
Magnetic ordering nonmagnetic
Electrical resistivity (20 °C) 1 µ Ω·m
Thermal conductivity (300 K) 18.6  W·m−1·K−1
CAS registry number 7440-14-4
Selected isotopes
Main article: Isotopes of radium
iso NA half-life DM DE (MeV) DP
223Ra  ? 11.43 d alpha 5.99 219Rn
224Ra  ? 3.6319 d alpha 5.789 220Rn
226Ra trace 1602 y alpha 4.871 222Rn
228Ra syn 6.7 y beta- 0.046 228Ac
References

Radium (IPA: /ˈreɪdiəm/) is a radioactive chemical element, which has the symbol Ra and atomic number 88 (see the periodic table). 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.

Contents

  • 1 Notable characteristics
  • 2 Applications
  • 3 History
  • 4 Occurrence
  • 5 Compounds
  • 6 Isotopes
  • 7 Radioactivity
  • 8 Precautions
  • 9 Further reading
  • 10 References
  • 11 External links

[edit] Notable characteristics

The heaviest of the alkaline earth metals, radium is intensely radioactive and resembles barium in its chemical behavior. 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 color), reacts violently with water and oil to form radium hydroxide and is slightly more volatile than barium. The normal phase of radium is a solid.

[edit] Applications

Some of the practical uses of radium are derived from its radiative properties. More recently discovered radioisotopes, such as 60Co and 137Cs, are replacing radium in even these limited uses because several of these are much more powerful, they are safer to handle, and they are more concentrated.

Radium was formerly used in self-luminous paints for watches, nuclear panels, 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 1950s. Objects painted with this paint 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 was also put in many foods for taste and as a preservative, but also exposed many people to radiation. 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 (usually in the form of radium chloride) is used in medicine to produce radon gas which in turn is used as a cancer treatment. The isotope 223Ra 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 226Ra (see Radioactivity).

[edit] History

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 consisting mostly of barium which gave a brilliant green flame color and crimson carmine spectral lines which had never been documented before. In 1902 radium was isolated into its pure metal by Curie and André-Louis 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:

Isotope
Radium emanation 222Rn
Radium A 218Po
Radium B 214Pb
Radium C 214Bi
Radium C1 214Po
Radium C2 210Tl
Radium D 210Pb
Radium E 210Bi
Radium F 210Po

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, anemia 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. The litigation and ultimate deaths of five "Radium Girl" employees who had used radium-based luminous paints on the dials of watches and clocks had a significant impact on the formulation of occupational disease labor law.

Handling of radium has been blamed for Marie Curie's premature death.

[edit] Occurrence

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 and 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.

[edit] Compounds

Its compounds color flames crimson carmine (rich red or crimson color 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.

See also radium compounds.

[edit] Isotopes

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.

[edit] Radioactivity

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. 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).

[edit] Precautions

[edit] Further reading