BERKELIUM (REVISED)

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

Overview

In the period between 1940 and 1961, eleven transuranium elements were discovered by researchers from the University of California at Berkeley (UCB). The term transuranium element refers to elements beyond uranium (atomic numbers greater than 92) in the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. All transuranium elements are unstable or radioactive. Radioactive elements throw off energy or particles as they decay into more stable atoms. One of these elements was berkelium.

Discovery and naming

In 1949, element number 97 was produced in a particle accelerator on the UCB campus. A particle accelerator is sometimes called an atom smasher. It is used to speed up very small particles and atoms, which then collide with atoms of such elements as gold, copper, or tin. These atoms are called targets. When the particles strike target atoms precisely, the atom is converted into a new element.

SYMBOL
Bk

ATOMIC NUMBER
97

ATOMIC MASS
247.0703

FAMILY
Actinide
Transuranium element

PRONUNCIATION
BER-klee-um

The UCB researchers fired alpha particles—helium atoms without their electrons—at ameririum atoms in their particle accelerator. The result was a new element—number 97.

The new element was given the name berkelium by the UCB research team, in honor of the city of Berkeley, where the research was done.

Physical and chemical properties

Berkelium exists in such small amounts that very little is known about its properties.

Occurrence in nature

Berkelium does not occur in nature. It is made artificially.

Isotopes

All isotopes of berkelium are radioactive. The most stable is berkelium-247. It has a half life of 1,380 years. 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. A radioactive isotope is one that breaks apart and gives off some form of radiation.

Berkelium-247 has a half life of 1,380 years. The half life of a radioactive element is the time it takes for half of a sample of the element to break down. After 1,380 years, only half of a 10-gram sample (5 grams) of berkelium-247 would be left. The other half would have changed into a different element. After another 1,380 years, half of the remaining berkelium-247 would have changed, leaving 2.5 grams behind.

Extraction

Berkelium does not occur in nature. Therefore, it is not extracted.

Uses

Berkelium has no commercial uses.

Compounds

No compounds of any practical importance have been prepared.

Health effects

The health effects of berkelium have not been studied in detail Since it is radioactive, scientists assume that it is harmful to human health.

Berkelium

melting point: 986°C
boiling point: Unknown
density: Unknown
most common ions: Bk³⁺, Bk⁴⁺

Berkelium, element 97, is a synthetic radioelement , first synthesized by Glenn Seaborg's group in 1949. A target of a few milligrams of an isotope of americium (²⁴¹Am) was bombarded with α -particles within a cyclotron at the University of California at Berkeley. An α -emitting species with a half-life of 4.5 hours was isolated via ion exchange chromatography and identified as being an isotope of element 97 with mass number 243. The first isolation of a berkelium compound was accomplished by Stanley Thompson and B. B. Cunningham in 1958. The known isotopes of berkelium have mass numbers that range from 240 to 251, and are all radioactive. The longest-lived isotope has a mass number of 247 and a half-life of 1,380 years. The ground state electronic configuration of the outer orbitals of berkelium is 5f ⁸6d ¹7s ². In compounds and in aqueous solution , berkelium is present in oxidation states III (the more stable) and IV.

Berkelium was named for the city in which it was discovered, in part to emphasize its relationship to its analog in the lanthanide series, terbium, which was named for the city of Ytterby in Sweden (where many of the rare earth minerals had been discovered). Metallic berkelium has a face-centered cubic structure—something it has in common with the actinide elements americium though einsteinium. Due to the very high level of radioactivity of even the long-lived isotopes, berkelium is usually studied at tracer level concentrations. The most commonly studied isotope is ²⁴⁹Bk, with a half-life of 320 days. This nuclide has been isolated at milligram levels and undergoes β -decay.

see also Actinium; Einsteinium; Fermium; Lawrencium; Mendelevium; Neptunium; Nobelium; Plutonium; Protactinium; Rutherfordium; Seaborg, Glenn Theodore; Thorium; Uranium.

Gregory R. Choppin

Bibliography

Choppin, Gregory R.; Liljenzin, Jan-Olov; and Rydberg, Jan (2001). Radiochemistry and Nuclear Chemistry, 3rd edition. Woburn, MA: Butterworth-Heinemann.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements Beyond Uranium. New York: Wiley-Interscience.

berkelium (symbol Bk) Radioactive metallic element, of the actinide series. It does not occur in nature and was first made in 1949 by alpha-particle bombardment of americium-241 at the University of California at Berkeley (after which it is named) by a research team led by the US nuclear chemist Glenn Seaborg (1912–99). Nine isotopes are known. Properties: at.no. 97; r.d. (calculated) 14; m.p. 986°C (1807°F); most stable isotope Bk²⁴⁷ (half-life 1.4×10³ yr).

ber·ke·li·um / bərˈkēlēəm/ • n. the chemical element of atomic number 97, an artificial radioactive metal of the actinide series. (Symbol: Bk)