Berkelium

no group (f-block) · period 7 · f-block · actinide

Identity

Name and symbol: Berkelium, Bk
Atomic number: 97 protons
Position: no group (f-block) · period 7 · f-block · actinide
CAS number: 7440-40-6

Atomic structure

Atomic mass: 247 u
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁹
[Rn] 7s²⁵f⁹
Electrons per shell: 2, 8, 18, 32, 27, 8, 2
Valence electrons: 11 ns, (n-1)d and (n-2)f

nuclide	half-life	decay
²⁴⁷Bk	1.38 ky	α≈100%; SF ?
²⁴⁹Bk	327.2 d	β-≈100%; α=0.00145±0.8%; SF=47e-9±0.2%
²⁴⁵Bk	4.95 d	ε=99.88±1%; α=0.12±0.1%
²⁴⁶Bk	1.80 d	β+≈100%; α ?

no stable isotope; the longest-lived nuclides

Physical properties

State at room temperature: Solid
Melting point: 1,323 K (1,049.85 °C)
Boiling point: 2,627 K (2,353.85 °C)
Density: 14 g/cm3
Appearance: silvery
Thermal conductivity: 10 W/(m·K)
Electrical resistivity: not in sources
Electrical conductivity: not in sources
Crystal structure: double hexagonal close packed
Molar heat capacity: not in sources

Chemical properties

Oxidation states: +4, +3
Electronegativity: 1.3 (Pauling Scale)
Ionisation energy: 6.23 eV
1st 601 kJ/mol
Electron affinity: not in sources
Atomic radius: van der Waals 244 pm
Ionic radius: Bk³⁺ 96; Bk⁴⁺ 83 pm

Reactivity: A silvery, radioactive actinide that behaves like its lanthanide analog terbium: +3 is the most stable state, especially in solution, +4 is found in solids such as BkO2 and BkF4 and in acid as the yellow Bk4+ ion, and +2 is uncertain.
with water: The sources do not describe the bulk metal with liquid water; both Bk(III) and Bk(IV) hydroxides are stable in 1 molar sodium hydroxide, and the hydrated chloride, nitrate and sulfate are known.
with oxygen, air: Does not react rapidly with oxygen at room temperature, probably because a protective oxide film forms; the oxides are brown BkO2 and yellow-green Bk2O3, obtained from the dioxide by hydrogen: $\ce{2 BkO2 + H2 -> Bk2O3 + H2O}$ .
with acids: Dissolves in aqueous inorganic acids with evolution of hydrogen to give green Bk3+ solutions; strong oxidants take it to Bk4+, yellow in hydrochloric and orange-yellow in sulfuric acid.
with halogens: Reacts with the halogens to binary halides; the trihalides BkF3, BkCl3, BkBr3 and BkI3 are the stable series, BkCl3 being made from the oxide with hydrogen chloride at about 500 C, and BkF4 is the only simple tetrahalide.

Typical compounds

BkO₂ berkelium dioxide brown, the tetravalent oxide
Bk₂O₃ berkelium(III) oxide yellow-green, melts at 1920 C
BkF₃ berkelium(III) fluoride yellow-green, two crystal forms
BkF₄ berkelium(IV) fluoride yellow-green solid isotypic with UF4
BkCl₃ berkelium(III) chloride green, first weighable berkelium compound (1962)

Occurrence, production and use

Crustal abundance: Not Applicable
Oceanic abundance: Not Applicable

Occurrence and sources

synthetic only made in reactors by neutron bombardment of plutonium-239

Extraction, production: Neutron bombardment of plutonium-239 in a reactor; first synthesis by 241Am (4He, 2n) 243Bk
nuclear reaction as printed by PubChem

Uses: not in sources

Safety, toxicity: not in sources

Discovery and name

Discovered by: Lawrence Berkeley National Laboratory
Discovered: 1949
First isolated: not in sources
Named by: not in sources
Origin of the name: after Berkeley, California, where it was discovered

Berkelium does not occur naturally in the Earth’s crust. It was first synthesized in December 1949 by Stanley G. Thompson, Glenn T. Seaborg, and Albert Ghiorso at the University of California in Berkeley using the nuclear reaction 241Am (4He, 2n) 243Bk in the Berkeley 60-inch cyclotron. The element was named for the town in California where it was first synthesized. The first isotope of berkelium produced from this experiment had a mass number of 243 and a half-life of 4.5 h. 247Bk has a half-life of 1.4×103 years, which makes it one of the least radioactive isotopes of berkelium. 249Bk has a half-life of 320 days, which makes it possible to isolate and study on a macroscopic scale, although studies have found that the radiation given off from berkelium creates health hazards. For example, lengthy exposure to the radiation from berkelium has been shown to cause an accumulation of berkelium in the skeletal system of rats. The radiation is also unfavorable to the formation of red blood cells [620], [621], [622], [623], [624]. Berkelium has no known isotopic applications aside from scientific research, in which it served as a target for the production of tennessine (Fig. IUPAC.97.1).

Conventions

Valence electrons are counted by the usual convention: the outer shell for s- and p-block elements, ns and (n-1)d for the d-block, ns, (n-1)d and (n-2)f for the f-block. Lanthanides and actinides are placed in the f-block with no group number. Electrical conductivity is the reciprocal of the printed resistivity. Ionic radii are Shannon effective radii, six-coordinate unless noted. Where a field reads “not in sources” the value was not found; it is a gap, not a zero. Regulatory limits are the published values and change often, so check the standard in force at your site and the numbers written into your own permit before you design to them.

Data

Element records, isotopes, radii and the descriptive text come from PubChem (NCBI), the Los Alamos National Laboratory periodic table, IUPAC CIAAW and the IAEA Atomic Mass Data Center. Appearance, thermal conductivity, electrical resistivity, crystal structure, discovery and the origin of each name come from Wikipedia and Periodic-Table-JSON, used under CC BY-SA 4.0. Hazard classifications come from the ECHA C&L inventory via PubChem. Ionic radii follow R. D. Shannon (1976). The water chapters cite their own sources at the foot of each entry, and are written to the level of Snoeyink and Jenkins, Stumm and Morgan, MWH's Water Treatment and Metcalf and Eddy.