Californium (Cf)
Element 98 · Actinide · atomic mass [251] u · f-block, period 7
Electron shells: 2, 8, 18, 32, 28, 8, 2
Californium is a prolific neutron emitter, and a single microgram releases millions of neutrons per second. That makes it genuinely useful despite costing millions per gram.
One microgram of californium-252 emits about 2.3 million neutrons every second.
- Atomic number
- 98
- Atomic mass
- [251] u
- Electron configuration
- [Rn] 7s² 5f¹⁰
- Group · period · block
- f-block · 7 · f
- Oxidation states
- +3
- Electronegativity
- 1.3 (Pauling)
- Melting point
- 900 °C
- Boiling point
- —
- Density
- Not measured
- State at 20 °C
- Solid
- Appearance
- Silvery metal
- Discovered
- Glenn T. Seaborg, Stanley Thompson, Kenneth Street Jr. and Albert Ghiorso, 1950
98 protons, and 98 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Shown in the strip below the table
What Californium is used for
- Portable neutron sources
- Detecting gold and silver ores
- Reactor start-up sources
- Airport and cargo scanning
Atomic structure of Californium
A neutral californium atom has 98 protons and 98 electrons. Its most common isotope carries about 153 neutrons, which is where the mass number 251 comes from. Change the neutron count and you have a different isotope of californium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 28, 8, 2. In orbital notation that is [Rn] 7s² 5f¹⁰. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Californium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Californium sits in the periodic table
The second f-block row, elements 89-103. All are radioactive, and everything past uranium is essentially man-made.
- One proton lighter: Berkelium.
- One proton heavier: Einsteinium.
Discovery and naming
Californium was discovered by Glenn T. Seaborg, Stanley Thompson, Kenneth Street Jr. and Albert Ghiorso in 1950. Its name comes from California and the University of California, which is also why its symbol (Cf) does not match its English name.
Every isotope of californium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Californium?
Californium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 251 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Californium have?
Californium has 98 protons, because the atomic number is the proton count and that is what makes an atom Californium at all. A neutral Californium atom has the same number of electrons, 98. The neutron count varies by isotope; the most common one has about 153, since 251 − 98 = 153.
What is the electron configuration of Californium?
The electron configuration of Californium is [Rn] 7s² 5f¹⁰. Its electrons are arranged 2, 8, 18, 32, 28, 8, 2 across 7 shells.
Is Californium a metal?
Yes. Californium is classified as a actinide, on the metallic side of the table.
What group and period is Californium in?
Californium sits in the f-block strip below the main table, in period 7, among the actinides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Californium?
Californium most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Californium?
Californium melts at 900 °C. That puts it in the solids at everyday temperatures.
What is Californium used for?
Portable neutron sources, Detecting gold and silver ores, Reactor start-up sources, Airport and cargo scanning. Californium is a prolific neutron emitter, and a single microgram releases millions of neutrons per second.
Who discovered Californium, and where does its name come from?
Californium (Cf) was discovered by Glenn T. Seaborg, Stanley Thompson, Kenneth Street Jr. and Albert Ghiorso in 1950. The name comes from California and the University of California.
Is Californium radioactive?
Yes. Every isotope of Californium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.