Holmium

Holmium is a chemical element with the symbol Ho and atomic number 67. It belongs to a group called the rare-earth elements and is part of the lanthanide series. Holmium is a soft, silvery metal that can bend easily and resists corrosion, but it is very reactive. When exposed to air, it slowly forms a yellowish coating and can burn when heated.

In nature, holmium is found together with other rare-earth metals, such as thulium. It is not very common, making up only 1.4 parts per million of the Earth's crust, about as common as tungsten. It was first discovered in 1878 by Swedish chemist Per Theodor Cleve, and also by Jacques-Louis Soret and Marc Delafontaine, who saw it spectroscopically. The name holmium comes from Holmia, the Latin name for Stockholm.

Holmium is mainly found in minerals like monazite and gadolinite and is usually extracted from monazite using special techniques. Its ions glow with a special light and are used in some lasers and to color glass. Holmium has the highest magnetic permeability and saturation of any element, making it useful for the strongest magnets. It can also absorb neutrons, so it is used in nuclear reactors to control reactions.

Properties

Holmium is the eleventh member of the lanthanide series. It appears in period 6 of the periodic table, between the lanthanides dysprosium and erbium, and above the actinide einsteinium.

Holmium is a soft, shiny metal that does not rust easily. It has special magnetic qualities, especially when cooled down. It can form strong magnetic materials when mixed with other metals like yttrium.

Holmium slowly changes when exposed to air, creating a layer that looks like rust on iron. It can burn to make holmium(III) oxide. It reacts with water and different gases to form new compounds, and it dissolves in acids to create solutions with yellow colors.

Holmium is most often found in a +3 oxidation state, but it can also exist in other states. Natural holmium is made of one stable type, holmium-165. Scientists have made many different types of holmium, some of which stay around for thousands of years and can be used to test machines that detect certain kinds of energy.

Compounds

Oxides and chalcogenides

Holmium(III) oxide is the only oxide of holmium. Its color changes depending on the lighting. In daylight, it looks yellowish. Under special light, it appears orange-red, similar to another oxide called erbium oxide. This color change happens because of how holmium ions give off light.

Holmium also forms other compounds called chalcogenides. One example is holmium(III) sulfide, which has orange-yellow crystals. It can form in different crystal shapes under high pressure. Holmium(III) sulfide is made by mixing holmium(III) oxide with hydrogen sulfide at high temperatures. Holmium also forms a compound called holmium(III) selenide, which has special magnetic properties at very low temperatures.

Halides

All four trihalides of holmium are known. Holmium(III) fluoride is a yellowish powder made by mixing holmium(III) oxide with ammonium fluoride. Holmium(III) chloride is made in a similar way, using ammonium chloride instead. These compounds have a special layered structure. Holmium also forms compounds with bromine and iodine, made by mixing holmium with these elements directly.

Organoholmium compounds

Main article: Organolanthanide chemistry

Organoholmium compounds behave similarly to compounds of other lanthanides. They mostly form ionic bonds and include certain types of chemical structures, such as cyclopentadienides and simple alkyls and aryls, some of which can form long chains.

History

Holmium was first noticed in 1878 by Swiss chemists who saw something unusual in a test. A Swedish chemist also found it while studying another material. He named the new discovery after his hometown, Stockholm. It took many years before scientists could fully separate and study this element.

Occurrence and production

Like all rare-earth elements, holmium is never found by itself in nature. Instead, it is mixed with other elements in minerals such as gadolinite and monazite. The main places where it is found are in China, the United States, Brazil, India, Sri Lanka, and Australia. Only about 10 kilograms of holmium are made each year.

Holmium is a very rare part of the Earth's crust, making up just 1.3 parts per million. It is also found in tiny amounts in soil, seawater, and almost not at all in the air. It is harder to separate holmium from other similar elements, but it can be taken from monazite sand using special methods.

Applications

Holmium is a special material that can be used in many important ways. For example, it helps scientists check how well machines that measure light work. It can also create very strong magnetic fields, which are useful in making tiny magnets.

Holmium is used in certain types of lasers that help doctors perform precise surgeries, like removing kidney stones. It can also be used to help treat some kinds of cancer and improve medical imaging. Scientists are even studying how it might help build future computers.

Biological role and precautions

Holmium does not play a role in human biology, but its salts can help speed up certain body processes. People usually get about a milligram of holmium each year from what they eat. Plants generally do not absorb much holmium from the soil. While some vegetables have been tested and found to contain small amounts of holmium, it is usually not a concern.

Holmium and its soluble salts can be harmful if eaten, but insoluble holmium salts are not dangerous. However, holmium dust can catch fire or cause explosions. If large amounts of holmium salts are breathed in, eaten, or put into the body, they can cause serious harm. The long-term effects of holmium on the body are still unknown, and it is considered to have low immediate harm when exposed for a short time.