Atomic number 102

Nobelium

No
+ phase
− phase

Shells Orbitals 5f 7s

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102 electrons in 7 shells: 2, 8, 18, 32, 32, 8, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Actinide
Period: 7
Block: f
Atomic mass: 259.10100 Da (longest-lived isotope)
Electron configuration: [Rn] 5f¹⁴ 7s²
Phase at 25 °C: solid
Melting point: 827 °C
Electronegativity (Pauling): 1.3
Discovered: 1966, Georgi Flerov's team at the Joint Institute for Nuclear Research, Dubna

Neighbours in the table

Md Lr

Nobelium honours Alfred Nobel, and its name is older than its discovery. In 1957 a Stockholm team at the Nobel Institute of Physics struck a curium-244 target with carbon-13 ions, according to Jefferson Lab. It announced a new element whose half-life, the time for half of a sample to decay, was 10 minutes. The name was assigned on that evidence and accepted by a commission of IUPAC (International Union of Pure and Applied Chemistry). That acceptance was premature, in Los Alamos’s words, because Russian and American work later ruled out any isotope of element 102 lasting 10 minutes.

Written as [Rn] 5f¹⁴ 7s², nobelium’s 102 electrons are shared out 2, 8, 18, 32, 32, 8 and 2 among the shells. Los Alamos lists oxidation states of 2 and 3, the charges each atom would carry if its bonds were fully ionic.

Nobelium is dipositive, meaning it takes the +2 oxidation state. Los Alamos notes that this sets it apart from lawrencium, the next element, which behaves more like the tripositive (+3) actinides before it. Removing one electron from a nobelium atom takes 6.62621 eV in NIST’s figure and 6.65 eV in Jefferson Lab’s. PubChem gives the mass of its longest-lived isotope, 259.10100 Da, that of nobelium-259.

Where it is found

Nobelium has no stable isotope, and it has no abundance in the crust or in the oceans. The contested Stockholm atoms of 1957 had come from a cyclotron, according to Jefferson Lab. Berkeley’s claim followed in April 1958, from A. Ghiorso, T. Sikkeland, J. R. Walton and G. T. Seaborg, Los Alamos’s archived page records. Their heavy-ion linear accelerator, the HILAC, fired carbon-12 ions at a thin curium target. That target was 95 per cent curium-244 and 4.5 per cent curium-246.

The nobelium came from curium-246 taking in a carbon-12 nucleus and shedding four neutrons. The team used a new double-recoil technique, according to Los Alamos. Proof came from a daughter nucleus. Fermium-250, which forms as element 102 decays and has a half-life of 30 minutes, was identified chemically, and Los Alamos’s archived page counts that identification as confirming nobelium’s production.

Why it matters

Rival claims to element 102 stood open until 1994, Los Alamos’s current page says. Work at the Kurchatov Institute in Russia in 1957 assigned an alpha radiation to it with a half-life between 2 and 40 seconds. That spread was too indefinite to support a discovery, in Los Alamos’s judgement. Berkeley’s group set out to confirm the Stockholm result, Jefferson Lab records, but made no 10-minute isotope. It made nobelium-254 instead.

Nobelium-254 lasted three seconds in Jefferson Lab’s account of that 1958 work. Berkeley’s confirmatory experiments of 1966 gave it 55 seconds, with 2.3 seconds for nobelium-252 and 23 seconds for nobelium-257, according to Los Alamos. Nobelium-254 lasts 51.2 seconds for the Atomic Mass Data Center (AMDC). A Russian figure of about 50 seconds, from 1963, proved right, Los Alamos’s current page says. IUPAC credits the first synthesis to Flerov’s team at Dubna, in 1966, but kept the established name.

Half of any nobelium-259 decays in roughly 58 minutes. It goes to fermium-255 by alpha emission, to mendelevium-259 by electron capture, or breaks up by spontaneous fission, the nucleus splitting unprompted. For the AMDC, 75 per cent of its decays are alpha emission, 25 per cent electron capture and under 10 per cent fission. The International Atomic Energy Agency (IAEA) evaluation gives 75, 25 and 10 per cent.

Properties

Properties of nobelium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	102
Atomic mass	259.10100 Da	Da	PubChem, longest-lived isotope
Melting point	827 °C	°C	Los Alamos: 827 °C
Electronegativity (Pauling)	1.3
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴
Phase at 25 °C	solid

This element has no standard atomic weight; the atomic mass shown is that of its longest-lived isotope, as PubChem gives it.

Safety

Nobelium’s hazard is ionising radiation, and Haz-Map, in PubChem’s safety record, classes it as a radiation hazard. No everyday form exists: only tiny amounts have ever been produced, according to Jefferson Lab. Its most stable isotope in that laboratory’s account, nobelium-259, is half gone in about an hour. Nobelium’s hazards are summarised in PubChem’s Laboratory Chemical Safety Summary for the element.

Questions

Who is nobelium named after?

Alfred Nobel, the inventor of dynamite, according to Los Alamos. The name came from the Nobel Institute of Physics in Stockholm, whose team claimed element 102 in 1957. IUPAC's Commission on Atomic Weights accepted it, too early as it turned out. IUPAC later gave the discovery to a team at Dubna but kept the name, which by then was in wide use in the scientific literature.

Who discovered nobelium?

IUPAC credits the first synthesis to Russian scientists of Dubna's Joint Institute for Nuclear Research, under Georgi Flerov, in 1966, and holds the claims made from 1957 onwards to be erroneous. Berkeley's work of 1958, by A. Ghiorso, T. Sikkeland, J. R. Walton and G. T. Seaborg, firing carbon-12 ions at curium, was the second of those claims. Los Alamos's current page dates IUPAC's decision to 1994.

How long does nobelium last?

Half of any nobelium-259 is gone after roughly 58 minutes, in Jefferson Lab's figures and in the evaluation of the International Atomic Energy Agency. Nobelium-255 lasts 3 minutes for Los Alamos and 3.52 minutes for the Atomic Mass Data Center (AMDC). None of its isotopes is stable, according to Jefferson Lab, and the Atomic Mass Data Center lists nuclides from nobelium-248 to nobelium-264. Nobelium-261 has an estimated half-life of 3 hours from the AMDC, not a measured one.

What is nobelium used for?

Nothing outside basic scientific research, Jefferson Lab says, since only tiny amounts of the element have ever been produced. Chemically, nobelium can be dipositive, taking the +2 oxidation state, which sets it apart from lawrencium, the element after it, in Los Alamos's account. PubChem gives the mass of its longest-lived isotope, nobelium-259, as 259.10100 Da.