Science / Periodic Table of Elements / Promethium (Pm): Atomic number: 61, Atomic mass: (147) g.mol -1, Electronegativity: unknown, Density: 6.475 g.cm-3 at 20°C, Melting point: 1168 °C, Boiling point: 2460 °C, Vanderwaals radius: unknown, Ionic radius: unknown, Isotopes: 9, Electronic shell: [ Xe ] 4f5 6s2, Energy of first ionisation: 534.6 kJ.mol -1, Energy of second ionisation: 1050 kJ.mol -1, Standard potential: - 2.42 V, Discovered by: Marinsky 1945. Promethium is a rare-earth metal that emits beta radius. It is very radoiactive and rare, so it is little studied: its chemical and physical properties are not well defined. Promethium salts have a pink or red colour that coluors the surroundings air with a pale blue-green light. Applications: Most promethium is used for research purpose. It can be used as beta radiation source in luminous paint, in nuclear batteries for guided missiles, watches, pacemakers and rados, and as a light source for signals. It is possible that in future it will be used as portable X-ray source. Promethium in the environment: Promethium dose occurs in the Earth's crust in tiny amounts in some uranium ores. It is not stable so it undergoes radioactive decay. All the promethium which might once have existed on Earth when it formed would have vanished within 10000 years.