Promethium is a chemical element in the Periodic Table marked with the atomic number of 61 and with the chemical symbol Pm. This chemical element belongs to period 6 elements and the Lanthanide category. Similar to the rest of the Lanthanide elements Promethium possesses some metallic properties. In the Periodic Table Promethium is preceded by Neodymium and is followed by Samarium.


Promethium has similar chemical and physical properties to Samarium and Neodymium. It forms salts when it’s mixed with other chemical elements. Among all Lanthanide elements Promethium has the third largest atomic radius. This chemical element does not occur freely in its natural solid state and can be extracted from other Lanthanide ores or produced through artificial synthesis. All Promethium isotopes have an extremely short half-life and Promethium is the only Lanthanide element, which does not have any stable isotopes. This chemical element has several commercial applications mainly in the electronics industry.



Physical Characteristics of Promethium

In terms of physical characteristics Promethium is a metallic element in a solid state. Promethium exists in a typical double hexagonal close-packed crystal structure. Due to the fact that this chemical element is quite unstable, it has not been fully studied by scientists. Although Promethium is a metallic element, some of its compounds tend to give off pink or reddish color hues. Promethium has notably high melting and boiling points, it is insoluble in water, but it gets dissolved in hydrochloric acid. Promethium is a paramagnetic element, which is moderately reactive. It forms mildly basic oxides in +2 and +3 oxidation states.


Chemical Properties of Promethium


Atomic Number – 61

Group – n/a

Period – 6

Block – f

Electronic Configuration – 4f5 6s2

Relative Atomic Mass – 145 (145 g/mol)

Molecular Weight – 145

Electronegativity – 1.13

Density (G CM-3) – 7.26 g/cm3 at room temperature

Melting Point – 1315 K; 1042 °C; 1908 °F

Boiling Point – 3273 K; 3000 °C; 5432 °F

Atomic Radius – 183 pm

Isotopes – 0

Electronic Shell – 2, 8, 18, 23, 8, 2


Discovery of Promethium

There were several inconclusive and incomplete discovery claims for Promethium throughout the years. Of all scientists and chemists working on the discovery of Promethium, the three physicists Chien Shiung Wu, Emilio Segrè, and Hans Bethe were credited with the discovery of the element in 1942. The very first isolation of Promethium was carried out in 1945. The element was named by Grace Mary Coryell after the Greek Titan Prometheus.


Recognized by:   Chien Shiung Wu, Emilio Segrè, and Hans Bethe

Known and discovered by: Chien Shiung Wu, Emilio Segrè, and Hans Bethe (1942)

Named by: Grace Mary Coryell (1945)


Uses and role of Promethium

Promethium has no known biological roles to humans and other living organisms. It has several uses in scientific researchers and a number of commercial applications in electronics.


Promethium is useful in signal lights and luminous paint. Another commercial application of this Lanthanide element is in atomic batteries where Promethium isotopes are converted into electric current. Other than that Promethium is also used in measuring devices in order to measure the thickness of various materials.


Promethium on Earth

Of all Lanthanide elements Promethium is one of the rarest ones found on Earth. This chemical element does not occur freely in nature in its solid, free state unless it is combined with other chemical elements and compounds. It can be found in some Europium ores in the Earth’s crust, but only in scarce amounts, which are barely traceable. However, Promethium can be synthesized and produced through alpha and beta decay of other elements, such as Uranium.


Apart from its lack of abundance on Earth, Promethium has also been discovered as part of the spectrum of the HR 465 star in the constellation Andromeda.



It has been discovered that this particular chemical element could make a change in the development of portable X-ray technology. It could also find future application in similar devices as a power or heat source for space satellites and space probes. However, at this point there are safer elements and materials acting as a substitute to Promethium and its compounds when it comes to such scientific and commercial applications.