Holmium (revised)

HOLMIUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Holmium occurs in Row 6 of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Elements with atomic numbers 58 through 71 are known as the lanthanides. The name comes from the element lanthanum. The lanthanides are also known as rare earth elements. Although lanthanides are not especially rare, they are very difficult to separate from each other.

Holmium was discovered by Swedish chemist Per Teodor Cleve (1840-1905) in 1879. He named the element after his birth-place, Stockholm, Sweden. Holmium occurs with other rare earth elements in minerals such as monazite and gadolinite. It can now be separated from other rare earth elements somewhat easily. But no major uses have been found for it or its compounds.

SYMBOL
Ho

ATOMIC NUMBER
67

ATOMIC MASS
164.9303

FAMILY
Lanthanide
rare earth metal)

PRONUNCIATION
HOL-me-um

Discovery and naming

In 1787, a lieutenant in the Swedish army named Carl Axel Arrhenius (1757-1824) was exploring a mine near Ytterby, Sweden. Arrhenius was a "rock hound," a person interested in the study of rocks and minerals. In his explorations, Arrhenius found a rock he had never seen before. He asked his friend Johan Gadolin (1760-1852), professor of chemistry at the University of Abo in Finland, to study it. Gadolin discovered in the rock a new mineral, which was given the name ytterite.

Ytterite proved to be a fascinating puzzle for chemists. The mineral contained a number of different "earths." In chemistry, the term earth refers to a naturally occurring compound of an element. For example, magnesia is a naturally occurring compound—an earth—of the element magnesium.

Chemists found the earths in ytterite all had very similar properties. However, they had trouble separating them from each other. In fact, it took more than a century to analyze ytterite completely.

In 1879, Cleve was studying an earth taken from yttria called erbia. Erbia had been regarded as a new element for some time. But Cleve separated erbia into three different parts. He called them erbia, holmia, and thulia. Holmia is the earth from which the element holmium comes. For his work, Cleve is given credit for the discovery of holmium.

In Cleve's time, chemical equipment was not very advanced. Chemists usually could not prepare very pure samples of materials. Ten years after the "discovery" of holmium, chemists realized it was actually holmium mixed with another new element, dysprosium.

Physical properties

Like other rare earth elements, holmium is a silvery metal that is soft, ductile, and malleable. Ductile means capable of being drawn into thin wires. Malleable means capable of being hammered into thin sheets. Both properties are common for metals. Holmium also has some rather unusual magnetic and electrical properties.

Holmium has a melting point of 1,470°C (2,680°F) and a boiling point of 2,720°C (4,930°F). Its density is 8.803 grams per cubic centimeter.

Chemical properties

Holmium metal tends to be stable at room temperature. In moist air and at higher temperatures, it becomes more reactive. For example, it combines with oxygen to form holmium oxide (Ho₂O₃), a yellow solid. Like most other metals, the element also dissolves in acids.

Occurrence in nature

The abundance of holmium in the Earth's crust is estimated to be about 0.7 to 1.2 parts per million. It is less common than most other rare earth elements, but more common than iodine, silver, mercury, and gold. The most common ores of holmium are monazite and gadolinite.

Isotopes

Only one naturally occurring isotope of holmium exists, holmium-165. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

At least 20 radioactive isotopes of holmium are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

Nonoe of the radioactive isotopes of holmium has any practical uses.

Extraction

Pure holmium is obtained by reacting calcium metal with holmium fluoride (HoF₃):

Pure holmium has been available only very recently.

Holmium lasers are used to reduce abnormal eye pressure and to treat glaucoma.

Uses

In the past there were almost no practical uses for holmium and its compounds. However, holmium is now used in specialized lasers. A laser is a device for producing very bright light of a single color. The kind of light produced in a laser depends on the elements of which it is made. Holmium lasers are used to reduce abnormal eye pressure, to treat glaucoma (an eye disorder), and to repair failed glaucoma surgeries.

Compounds

Few holmium compounds have any important commercial uses.

Health effects

Almost nothing is known about the health effects of holmium. In such cases, the usual recommendation is to treat the element as if it were highly toxic.