ActinideElement 97 · f-block

Berkelium (Bk)

Berkelium (Bk) is an actinide with atomic number 97; its most stable known isotope has mass number 247. At room temperature it is a solid that melts at 986 °C.

97BkBerkelium[247]

Atomic number

protons

Atomic weight

[247]

most stable isotope

Melting point

986 °C

1,259.15 K

Boiling point

—

Density

14.78 g/cm³

near room temperature

Electronegativity

1.3

Pauling scale

State at 25 °C

Solid

Discovered

1949

United States (Berkeley)

Berkelium at a glance

Identity

Symbol	Bk
Atomic number (Z)	97
Atomic weight	[247] mass number of the most stable isotope
Category	Actinide
Group	— (f-block: actinide series)
Period	7
Block	f-block
CAS number	7440-40-6

Atomic properties

Electron configuration	[Rn] 5f⁹ 7s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁹ 6s² 6p⁶ 7s²
Electrons per shell	2, 8, 18, 32, 27, 8, 2
Oxidation states	+3 Less common: +2, +4, +5
Electronegativity (Pauling)	1.3
First ionisation energy	6.198 eV (598 kJ/mol) 2nd: 11.9 eV · 3rd: 21.6 eV
Covalent radius	168 pm
Van der Waals radius	244 pm

Physical properties

State at 25 °C	Solid
Melting point	986 °C · 1,806.8 °F · 1,259.15 K
Density	14.78 g/cm³

Isotopes & abundance

Natural occurrence	Synthetic
Radioactive	Yes
Most stable isotope	²⁴⁷Bk — half-life 1.38 thousand years
Known isotopes	22

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Berkelium electron configuration

Berkelium has 97 electrons. Written in short form, its ground-state configuration is [Rn] 5f⁹ 7s² — the electrons of the noble gas radon, plus 5f⁹ 7s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁹ 6s² 6p⁶ 7s².

5f↑↓↑↓↑↑↑↑↑

7s↑↓

Discovery and name

Discovered

1949 — Stanley G. Thompson, Albert Ghiorso and Glenn T. Seaborg · United States (Berkeley).

Name

Berkeley, California.

Known for

Made only in tiny amounts in reactors; used as a target to make heavier elements such as tennessine.

Isotopes of berkelium

Berkelium has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
²⁴⁷Bk	97	150	1.38 thousand years

22 isotopes of berkelium are known in our data set (half-lives as published in nuclear data tables).

Berkelium and its neighbours in the actinide series

Neighbouring elements in the same f-block series:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Plutonium	94	[244]	640 °C	3,228 °C	19.7 g/cm³	1.28
Americium	95	[243]	1,176 °C	—	12 g/cm³	1.3
Curium	96	[247]	1,345 °C	—	13.51 g/cm³	1.3
Berkelium	97	[247]	986 °C	—	14.78 g/cm³	1.3
Californium	98	[251]	900 °C	—	15.1 g/cm³	1.3
Einsteinium	99	[252]	860 °C (est.)	—	8.84 g/cm³ (pred.)	1.3
Fermium	100	[257]	1,527 °C (est.)	—	9.7 g/cm³ (pred.)	1.3

Frequently asked questions

6 answers

What is the atomic mass of berkelium?

Berkelium has no stable isotopes, so it has no standard atomic weight. Periodic tables show [247], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does berkelium have?

A neutral berkelium atom has 97 protons and 97 electrons. Its most stable isotope, berkelium-247, has 150 neutrons.

What is the electron configuration of berkelium?

[Rn] 5f⁹ 7s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁹ 6s² 6p⁶ 7s²).

What are the melting and boiling points of berkelium?

Berkelium melts at 986 °C (1,806.8 °F).

Is berkelium a metal?

Berkelium is a metal. It is in the f-block, period 7, and is a solid at room temperature.

Who discovered berkelium?

1949 — Stanley G. Thompson, Albert Ghiorso and Glenn T. Seaborg (United States (Berkeley)).