Radium

Radium: the essentials

 pure metallic radium is brilliant white when freshly prepared, but blackens on exposure to air, probably due to formation of the nitride. It exhibits luminescence, as do its salts; it decomposes in water and is somewhat more volatile than barium. Radium imparts a carmine red colour to a flame.

Radium emits α, β, and γ rays and when mixed with beryllium produces neutrons. Inhalation, injection, or body exposure to radium can cause cancer and other body disorders. alkaline earth metal, white but tarnishes black upon exposure to air, luminesces, decomposes in water, emits radioactive radon gas, disintegrated radioactively until it reaches stable lead, radiological hazard, α, β, and γ emitter, exposure to radium can cause cancer and other body disorders. Radium is over a million times more radioactive than the same mass of uranium.

Radium was discovered in 1898 by Marie and Pierre Curie in pitchblende (or uraninite) from North Bohemia. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride, employing a mercury cathode. On distillation in an atmosphere of hydrogen this amalgam yielded the pure metal.

This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Isolation

all isotopes of radium are radioactive and there is only ever any need to make radium metal on very small scales for research purposes. Radium is extremely scarce but found in uranium ores such as pitchblende at slightly more than 1g in 10 tonnes of ore. It may be made on very small scale by the electrolysis of molten radium chloride, RaCl₂. This was first done using a mercury cathode, which gave radium amalgam. The metal was obtained by distillation away from the amalgam.

cathode: Ra²⁺(l) + 2e^- → Ra

anode: Cl^-(l) → ¹/₂Cl₂ (g) + e^-

Ionisation Energies

This section includes ionisation energies of radium.

Electronic configuration

The following represents the electronic configuration and its associated term symbol for the ground state neutral gaseous atom. The configuration associated with radium in its compounds is not necessarily the same.

• Ground state electron configuration:  [Rn].7s²
• Shell structure:  2.8.18.32.18.8.2
• Term symbol:   ¹S₀

Reaction of radium with air

Radium is a silvery white metal. The surface of radium metal is covered with a thin layer of oxide that helps protect the metal from attack by air, but to a lesser extent than the corresponding layer in magnesium. I'm not sure if this reaction has been done, but once ignited, radium metal is likely to burn in air to give a mixture of white radium oxide, RaO, and radium nitride, Ra₃N₂. The superoxide RaO₂ is also likely to form in this reaction. Radium, four places below magnesium in the periodic table is more reactive with air than magnesium.

2Ra(s) + O₂(g) → 2RaO(s)

Ra(s) + O₂(g) → RaO₂(s)

3Ra(s) + N₂(g) → Ra₃N₂(s)

Reaction of radium with water

Radium probably reacts very readily with water to form radium hydroxide, Ba(OH)₂ and hydrogen gas (H₂). The reaction is expected to be quicker than that of barium (immediately above radium in the periodic table).

Ra(s) + 2H₂O(g) → Ra(OH)₂(aq) + H₂(g)

Reaction of radium with the halogens

I'm not sure that radium has been reacted directly with the halogens, although certainly two of the expected products radium(II) chloride and radium(II) bromide are known.

Here is some information about the crystal structure of radium.

• Space group: Im-3m (Space group number: 229)
• Structure: bcc (body-centred cubic)
• Cell parameters:
  • a: 514.8 pm
  • b: 514.8 pm
  • c: 514.8 pm
  • α: 90.000°
  • β: 90.000°
  • γ: 90.000°

The most used definition of electronegativity is that an element's electronegativity is the power of an atom when in a molecule to attract electron density to itself. The electronegativity depends upon a number of factors and in particuler as the other atoms in the molecule. The first scale of electronegativity was developed by Linus Pauling and on his scale radium has a value of 0.9 on a scale running from from about 0.7 (an estimate for francium) to 2.20 (for hydrogen) to 3.98 (fluorine). Electronegativity has no units but "Pauling units" are often used when indicating values mapped on to the Pauling scale. On the interactive plot below you may find the "Ball chart" and "Shaded table" styles most useful.

Radium is found naturally in uranium ores such as pitchblende (mostly UO₂). One tonne of pitchblende might yield about 0.15 g of radium. Ores containing radium are found in Zaire, Australia, Canada, and USA (New Mexico, Utah, and in small amounts in carnotite sands from Colorado). Recovery is costly. Some estimates suggest that every square kilometre of soil to a depth of a 40 cm contains about 1 g of radium.

Abundances of radium in various environments

In this table of abundances, values are given in units of ppb (parts per billion; 1 billion = 10⁹), both in terms of weight and in terms of numbers of atoms. Values for abundances are difficult to determine with certainty, so all values should be treated with some caution, especially so for the less common elements. Local concentrations of any element can vary from those given here an orders of magnitude or so and values in various literature sources for less common elements do seem to vary considerably.

Radiosotope data

Fluorides

• RaF₂:

  thermochemical cycle: (no value) kJ mol^-1

  calculated: 2284 kJ mol^-1

Chlorides

• RaCl₂:

  thermochemical cycle: (no value) kJ mol^-1

  calculated: 2004 kJ mol^-1

Bromides

• RaBr₂:

  thermochemical cycle: (no value) kJ mol^-1

  calculated: 1929 kJ mol^-1

Iodides

• RaI₂:

  thermochemical cycle: (no value) kJ mol^-1

  calculated: 1803 kJ mol^-1

Temperatures

• Melting point: 973 [or 700 °C (1292 °F)] K
• Boiling point: 2010 [or 1737 °C (3159 °F)] K (liquid range: 1037  K

Expansion and conduction properties

• Thermal conductivity: 19  W m^-1 K^-1

Bulk properties

• Density of solid: 5000  kg m^-3
• Molar volume: 41.09  cm³

Enthalpies

• Enthalpy of fusion: about 8  kJ mol^-1
• Enthalpy of vaporisation: about 125  kJ mol^-1
• Enthalpy of atomisation: 159  kJ mol^-1

Thermodynamic data

The following uses for radium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).

• self-luminous paints
• neutron sources
• medical uses for the treatment of conditions such as cancer (now being replaced by ⁶⁰Co sources)