Holmium is a rare earth element, one of the elements found in Row 6 of the periodic table between Groups 2 and 3. Its atomic number is 67, its atomic mass is 164.9303, and its chemical symbol is Ho.

Properties

Holmium is a silvery metal that is soft, ductile, and malleable. It has a melting point of 2,680°F (1,470°C), a boiling point of 4,930°F (2,720°C), and a density of 8.803 grams per cubic centimeter. It tends to be chemically stable at room temperature, but becomes more active at higher temperatures when, for example, it reacts with oxygen to form holmium oxide (Ho₂O₃).

Occurrence and Extraction

The abundance of holmium in the Earth's crust is estimated to be about 0.7-1.2 parts per million, making it less common than most other rare earth elements, but more common than some familiar elements, such as iodine, silver, mercury, and gold. The most common ores of holmium are monazite and gadolinite. Holmium is extracted from its ores by heating calcium metal with holmium fluoride: 3Ca + 2HoF₃ 3CaF₂ + 2 Ho.

Discovery and Naming

Holmium was discovered in 1879 by the Swedish chemist Per Teodor Cleve (1840-1905). Cleve found the new element in a mineral called ytterite that had been discovered nearly a century earlier by a Swedish army officer, Carl Axel Arrhenius (1757- 1824). Ytterite was the subject of considerable research on the part of chemists and mineralogists and was eventually to yield nine new elements. Cleve named the new element after his birthplace, Stockholm.

Uses

Holmium has very few practical purposes, one exception being in the manufacture of specialized types of laser. Holmium lasers are now used to some extent in eye surgery where they are used to treat glaucoma and reduce abnormal eye pressure.