Rutherfordium – facts and properties
- Symbol
- Rf
- Atomic number
- 104
- Atomic mass
- 267 u
- Period
- 7
- Group
- 4
- Category
- transition metal
- Electron configuration
- [Rn] 5f¹⁴ 6d² 7s²
- Valence electrons
- 4
- State at standard conditions
- solid
- Discovered
- 1964
Rutherfordium has atomic number 104 and is an artificial, radioactive element. It opens the transactinoids, the elements beyond the actinoid series, and counts among the superheavy elements. Accelerators produce it atom by atom. It is also remembered for a decades-long quarrel between research groups in the Soviet Union and the United States over who made it first. Almost all of its properties are still only predicted.
Position in the periodic table
Occurrence and extraction
Rutherfordium exists only artificially. Its known isotopes are short-lived. Some halve within fractions of a second, and the longest-lived, rutherfordium-267, is reported at roughly an hour. Very few of its decays have been seen, so that figure is uncertain.
The discovery is the best-known chapter of the Transfermium Wars. Transfermium elements are all those beyond fermium, and from the 1960s to the 1990s two camps argued over who had first detected the earliest of them. The team around Georgy Flerov at Dubna in the Soviet Union reported in 1964 that it had made the element by bombarding plutonium with neon ions. Its evidence was spontaneous fission, a decay in which a nucleus breaks apart with no outside trigger. Dubna proposed the name kurchatovium, after the Soviet nuclear physicist Igor Kurchatov.
In 1969 a group around Albert Ghiorso at Berkeley reported that it had produced the element from californium and carbon ions. Its proof rested on alpha decays whose daughter nuclei were already known, so the events could be assigned unambiguously. Berkeley chose the name rutherfordium. Each side doubted the other's results. A joint working group of the international unions IUPAC and IUPAP assessed the claims in the early 1990s and divided the credit largely between the camps. The naming also dragged on, because a proposal of 1994 would have given the name rutherfordium to element 106. Only in 1997 did IUPAC fix the names in use today.
The element honours Ernest Rutherford. The New Zealand-born physicist recognised in 1911 that an atom has a tiny, positively charged nucleus.
Properties and reactions
Rutherfordium is in period 7 and group 4, below hafnium. The atomic mass is given as 267 u, the mass number of rutherfordium-267. Nobody has ever seen a sample of the metal. Melting point, boiling point, density and electronegativity are unknown, and calculations offer only estimates. They suggest a metal considerably denser than hafnium.
The electron configuration [Rn] 5f¹⁴ 6d² 7s² is predicted. It mirrors that of hafnium, one shell further out. So rutherfordium is expected to resemble zirconium and hafnium and to be most stable in the oxidation state plus four. Relativistic effects might still bring deviations.
Experiments on a few atoms support the expectation. In the gas phase rutherfordium forms a volatile chloride, and in aqueous solution its fourfold positive ion behaves like the ions of zirconium and hafnium, not like the tetravalent actinoids. These measurements rest on a few atoms and allow only coarse conclusions.
The isotopes decay by alpha radiation or spontaneous fission. The element itself is no hazard, since it exists only in minute amounts and only briefly.
Research and synthesis
Rutherfordium has no application beyond research. It does mark an important threshold in nuclear physics. By the simple liquid-drop picture of the nucleus, nuclei of this size should barely resist fission. That they exist with measurable lifetimes is owed to shell effects, a layered structure of protons and neutrons inside the nucleus that resembles the build-up of the electron shell. Rutherfordium isotopes therefore serve as test cases for nuclear models.
The element is made in fusion reactions, for example by firing titanium-50 at lead-208 or neon-22 at plutonium-244. A separator picks out the atoms, and their decay chains identify them.
Quick question
What is the atomic number of rutherfordium (Rf)?
FAQ
Who discovered rutherfordium?
People argued about it for decades. Groups at Dubna and Berkeley both claimed it, and an international working group split the credit largely between them. The name comes from Berkeley.
What are the properties of rutherfordium?
Hardly anything has been measured. The expectation rests on its place below hafnium: a heavy metal with the oxidation state plus four. A few experiments on small numbers of atoms support that.
What is rutherfordium used for?
It has no application. In research it is used to check whether nuclear models for superheavy elements are right, and to refine methods for studying an element atom by atom.