Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Holmium, symbol Ho, silver-colored metallic element with an atomic number of 67. Holmium is one of the most paramagnetic substances known (see Magnetism). The element has few practical applications, though it has been used in some electronic devices and as a catalyst in industrial chemical reactions (see Catalysis).

Holmium was discovered in 1878 by the Swiss chemists Jacques Louis Soret and Marc Delafontaine, and, independently, by the Swedish chemist Per Teodor Cleve in 1879. Cleve named the element after his native city of Stockholm, Sweden (the latinized name of Stockholm is Holmia).

Holmium is one of the least abundant of the rare earth metals, ranking 55th in order of abundance of the elements in the earth's crust. Holmium has an atomic weight of 164.93. It melts at about 1474° C (about 2685° F), boils at about 2700° C (about 4892° F), and has a specific gravity of 8.8. Holmium occurs in gadolinite and other minerals containing rare earths. Holmium oxide, a grayish-white powder, and a few salts, such as the sulfate, have been prepared.