Nobelium – facts and properties
- Symbol
- No
- Atomic number
- 102
- Atomic mass
- 259 u
- Period
- 7
- Category
- actinide
- Electron configuration
- [Rn] 5f¹⁴ 7s²
- Electronegativity
- 1.3
- Valence electrons
- 16
- State at standard conditions
- solid
- Melting point
- 827 °C
- Discovered
- 1957
Nobelium is a radioactive element made only in accelerators, with atomic number 102. It is named after Alfred Nobel, the inventor of dynamite and founder of the Nobel Prizes. Its discovery was disputed for a long time: the report from Stockholm in 1957 could not be confirmed, Berkeley and Dubna reached results of their own later, and only in the 1990s did experts settle the order of priority. Chemically nobelium is an exception among the actinoids, because its most stable oxidation state is plus two.
Position in the periodic table
Occurrence and extraction
Nobelium exists only as a man-made element. The longest-lived known isotope, nobelium-259, has a half-life of about an hour, and many other isotopes last only seconds or minutes.
The discovery is a story with three parties. The first report came from Stockholm in 1957. An international group at the Nobel Institute reported that it had made element 102 by bombarding curium with carbon ions. It proposed the name nobelium. Neither Berkeley nor Dubna could reproduce this. In 1958 Albert Ghiorso, Glenn Seaborg and their colleagues in Berkeley also bombarded curium with carbon ions and claimed the element for themselves. In parallel, the group around Georgy Flerov worked in Dubna. The expert panel that later assessed the priority questions saw convincing evidence only in the Dubna experiments of 1966.
The name nobelium nevertheless stayed. The Dubna researchers had suggested joliotium, but in 1997 the International Union of Pure and Applied Chemistry confirmed nobelium, which had been used in the literature for decades.
Today nobelium isotopes are made in accelerators. Heavy ions hit a thin target, for example calcium-48 on lead-208, and the nuclei fuse. What results are single atoms.
Properties and reactions
Nobelium is in period 7 and is the fourteenth actinoid, in the actinoid row between mendelevium on its left and lawrencium on its right. Ytterbium sits above it in the lanthanoid row. The electron configuration [Rn] 5f¹⁴ 7s² shows a completely filled 5f shell. The electronegativity of 1.3 and the melting point of 827 °C are estimates, since there has never been a sample of the metal. Its atomic mass is given as 259 u, the mass number of the longest-lived isotope, nobelium-259.
The filled 5f shell explains the exception. When nobelium gives up its two 7s electrons, the ion No²⁺ remains with the especially stable, completely filled 5f shell. Ytterbium above it behaves similarly, since there too the divalent state is readily reached once the 4f shell is full. Trivalent nobelium is obtained only with strong oxidising agents. Even in early experiments with minute amounts, No²⁺ behaved in an ion-exchange column much like calcium and strontium ions.
The isotopes decay mainly by alpha radiation, some also by electron capture or spontaneous fission. Since only single atoms are present, a hazard from the element itself plays practically no role.
Research and synthesis
Nobelium has no use outside research. It serves as a proving ground for working with the heaviest elements, because its isotopes can be made in reactions similar to those that produce the superheavy elements. Separation techniques, detection methods and computer models are tested on nobelium.
At GSI in Darmstadt in 2016, nobelium was studied with laser light for the first time. The spectrum of single atoms reveals the energy levels of the electrons. Because the electrons of heavy atoms move at high speed, relativistic effects come into play, and such measurements check whether theory captures them correctly. In 2025 a team in Berkeley also identified molecules containing nobelium directly, in which water or nitrogen had attached to the atom.
Whether nobelium can ever be made in a visible amount is an open question, since the half-lives are short and the yields small.
Quick question
What is the atomic number of nobelium (No)?
FAQ
Why is it called nobelium, although the first report was wrong?
It is named after Alfred Nobel, the Swedish chemist and inventor who endowed the Nobel Prize. The name comes from the Stockholm report, which was not confirmed, and it was kept all the same.
Who discovered nobelium?
That was disputed for a long time. Groups in Stockholm, Berkeley and Dubna all made claims. The international assessment finally saw the convincing evidence in the Dubna experiments.
Why is plus two the most stable state of nobelium?
After two electrons are given up, a completely filled 5f shell remains, and that is especially stable. It is an exception, because the other late actinoids are mostly trivalent.