Science / Periodic Table of Elements / Holmium (Ho): Atomic number: 67, Atomic mass: 164.9 g.mol -1, Electronegativity: 1.2, Density: 8.8 g.cm-3 at 20°C, Melting point: 1474 °C, Boiling point: 2695 °C, Vanderwaals radius: unknown, Ionic radius: unknown, Isotopes: 4, Electronic shell: [ Xe ] 4f11 6s2, Energy of first ionisation: 580 kJ.mol -1, Energy of second ionisation: 1136.6 kJ.mol -1, Standard potential: - 2.32 V, Discovered: J.L. Soret in 1878. Holmium is a melleable, soft, lustrous metal with a silvery colour, belonging to the lantanides series of the periodic chart of elements. It is slowly attacked by oxygen and water and dissolves in acids. It is stable in dry air at room temperature. Applications: Holmium alloys are used as a magnetic flux concentrator to create the strongest artificially-generated magnetic fields. It is also used in nuclear reactors for nuclear control rods. Holmium oxide is used as yellow gas colouring. Holmium in the environment: Holmium is one of the rarer of the rare-earth elements but is, nevertheless, 20 times more abundant than silver. Like all other rare earths, holmium is not naturally found as free element. It is found in minerals such as monazite and bastanasite, even if it is just a minor components of such ores. World production of holmium is around 10 tonnes per year and main mining areas are China, USA, Brazil, India, Sri Lanka and Australia. Reserves of holmium are hestimated to be around 400.000 tonnes. Health effects of holmium: Holmium has no biological role and it is considered one of the least abundant elements present in human body. It has been noted that holmium stimulates metabolism, even if it appears to have a low acute toxic rating. Environmental effects of holmium: Holmium poses no environmental therat to plants and animals.