Radium is the only radioactive element of the alkaline earth metals. It is also the rarest of this group, and forms in small amounts when atoms of more common metals, such as uranium and thorium, decay. Radium atoms do not survive for long, and most of them quickly decay into radon, a radioactive noble gas.
This element is highly dangerous and is rarely used today. However, in the early 20th century, radium compounds were in common use. Luminous paints, such as those used to make watch dials glow in the dark, were created with radium. People working with this paint often became ill, especially with cancer, because the radiation produced by radium damages DNA. However, until the 1940s, many people thought that the radioactivity of radium was not harmful, quite the contrary.
Summary of properties (Ra)
| Atomic weight | [226] |
| Discoverer (year) | Curie, Marie & Pierre (1898) |
| Natural form | metallic solid (body centered cubic) |
| Electron configuration | [Rn] 7s2 |
| Melting point (ºC) | 700 |
| Boiling point (ºC) | 1737 |
| Abundance in earth's crust (ppm) | <0.001 |
| Isotope (abundance) | |
| Density g/cm3 | 5.5 |
| Van der Waals radius (pm) | 283 |
| Covalent radius (pm) | 211 |
| Electronegativity (Pauling) | 0.89 |
| Vaporization enthalpy (kJ/mol) | 136.80 |
| Enthalpy of fusion (kJ/mol) | 7.15 |
| Specific heat capacity (J/g·K) at 25ºC and 1 atm | - |
| Thermal conductivity (W/cm·K) at 25ºC and 1 atm | - |
| Oxidation state | +2 |
| Electron affinity (eV) | |
| 1st Ionization potential (eV) | 5.2784 |
