Atomic number 104

Rutherfordium

Rf
+ phase
− phase

Shells Orbitals 5f 6d 7s

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104 electrons in 7 shells: 2, 8, 18, 32, 32, 10, 2.

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

Category: Transition metal
Period: 7
Group: 4
Block: d
Atomic mass: 267.122 Da (longest-lived isotope, estimated)
Electron configuration: [Rn] 5f¹⁴ 6d² 7s² (predicted)
Phase at 25 °C: solid (predicted)
Discovered: 1964, Joint Institute for Nuclear Research, Dubna (credit still debated with Berkeley, 1969)

Neighbours in the table

Lr Db

Element 104 was claimed twice, five years apart, by two rival laboratories. A group at Dubna’s Joint Institute for Nuclear Research, then in the Soviet Union, reported it first, in 1964. In 1969 a Berkeley team of Ghiorso, Nurmia, Harris and the two Eskolas reported two isotopes positively identified and possibly a third, Los Alamos records. Credit for the discovery is still under debate, in Jefferson Lab’s words. The name honours Ernest Rutherford, Los Alamos records.

Rutherfordium is the first transactinide, the first element past the actinide series. Predictions place its 104 electrons in shells of 2, 8, 18, 32, 32, 10 and 2, giving the configuration [Rn] 5f¹⁴ 6d² 7s². Rutherfordium sits in group 4, beneath hafnium, just after the f block, which Chem1 places between groups 3 and 4.

Its predicted oxidation state, a bookkeeping charge that treats every bond as ionic, is +4 for both Jefferson Lab and Los Alamos, and Los Alamos also gives +3. Its first ionisation energy, the energy needed to remove one electron from an isolated atom, is a theoretical 6.02 electronvolts (a unit of energy for single particles) in NIST’s table. PubChem gives the mass of its longest-lived isotope, 267.122 Da, the mass NIST tabulates for rutherfordium-267.

Where it is found

Rutherfordium has no crustal or oceanic abundance. In both discovery accounts, accelerated ions fired at a heavy target made the atoms.

At Dubna in 1964, plutonium-242 was bombarded with neon-22 ions accelerated to 113 to 115 MeV. Fission tracks in a special glass, measured under a microscope, revealed an isotope that splits spontaneously, Los Alamos reports. The half-life, the time for half the atoms to decay, was 0.3 seconds, possibly from rutherfordium-260. Later Soviet data cut that figure to 0.15 seconds. The Atomic Mass Data Center gives rutherfordium-260 21 milliseconds.

Berkeley lacked the equipment to accelerate neon ions, Jefferson Lab explains, so its group fired carbon-12 and carbon-13 nuclei at californium. The targets were californium-248 and -249, Jefferson Lab says, and Los Alamos gives the carbon-12 nuclei 71 MeV and the carbon-13 nuclei 69 MeV. Rutherfordium-257 formed with the instant emission of four neutrons, and rutherfordium-259 with three. Rutherfordium-257 decays by alpha emission into nobelium-253, half-life 105 seconds, and rutherfordium-259 into nobelium-255, 185 seconds, Los Alamos records. Thousands of atoms of the two have now been detected, Los Alamos notes.

Why it matters

Rutherfordium-257 halves in 4 to 5 seconds and rutherfordium-259 in 3 to 4, both by alpha emission in Los Alamos’s account. Rutherfordium-257’s half-life is 5.0 seconds in the Atomic Mass Data Center’s figures. Its decays are 89.3 per cent alpha, 1.3 per cent spontaneous fission and 9.4 per cent beta-plus, in which a proton becomes a neutron, emitting a positron. For 259 it gives 2.63 seconds, 85 per cent alpha, 15 per cent beta-plus and under 3 per cent fission.

Longer-lived isotopes were found in 2003 and 2004. Rutherfordium-263 is the most stable isotope for Jefferson Lab, at about 10 minutes, decaying by spontaneous fission. In IAEA’s evaluation its half-life is 10 minutes with a 30 per cent alpha branch alongside fission; the Atomic Mass Data Center gives 11. Rutherfordium-267’s half-life is 1.3 hours in IAEA’s evaluation, fission 100 per cent and alpha 33.3 per cent, and 2.5 hours for the Atomic Mass Data Center.

Los Alamos expects rutherfordium to share hafnium’s chemistry and to form a relatively volatile tetrachloride, a chlorine compound. Dubna tried to show that the 0.3-second activity was more volatile than the relatively nonvolatile actinide trichlorides. The test gave important evidence without separating the element from all others. Its melting point is predicted at 2100 °C and its boiling point at 5500 °C by Los Alamos.

Properties

Properties of rutherfordium 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	104
Atomic mass	267.122 Da	Da	PubChem, longest-lived isotope, estimated
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴ 6d² (predicted)
Phase at 25 °C	solid (predicted)

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

That mass is an estimate by the IAEA's Atomic Mass Data Center, not a measurement.

The electron configuration and the phase of this element are predictions, not measurements.

Safety

Rutherfordium’s hazard is ionising radiation: it has no stable isotope, and its isotopes decay by alpha emission, beta-plus decay or spontaneous fission. Only small amounts have ever been produced, and none lasts long, in Jefferson Lab’s account, so there is none to handle. PubChem’s record for element 104 is the reference for the substance.

Questions

Who discovered rutherfordium?

Two groups claim it. Physicists at Dubna, in the Soviet Union, reported element 104 in 1964 after firing neon-22 ions at plutonium-242. Albert Ghiorso's Berkeley team reported isotopes 257, 258 and 259 in 1969, with 261 as well in Jefferson Lab's list. Berkeley could not make Dubna's isotope, according to Jefferson Lab. The credit remains under debate.

What is rutherfordium named after?

Rutherfordium honours Ernest Rutherford, according to Los Alamos. The name went to element 104, which Dubna reported in 1964 and Berkeley in 1969. Rutherfordium sits in period 7 and group 4, in the d block, under hafnium, and carries the symbol Rf. Every one of its isotopes is radioactive: Jefferson Lab counts no stable ones, and the longest-lived last minutes to hours.

What is the most stable isotope of rutherfordium?

Jefferson Lab names rutherfordium-263 as the most stable, with a half-life of about 10 minutes, decaying by spontaneous fission; IAEA's evaluation gives it 10 minutes with a 30 per cent alpha branch. Rutherfordium-267 has a longer half-life: 1.3 hours in IAEA's evaluation, by fission with a 33.3 per cent alpha branch, and 2.5 hours in the Atomic Mass Data Center's. PubChem gives the mass of its longest-lived isotope, 267.122 Da, that of rutherfordium-267.

What is rutherfordium used for?

Nothing outside basic scientific research, Jefferson Lab says, because so little is produced and its half-life is short. Its atoms still answer questions. Rutherfordium-258 turned up in the 1982 discovery of meitnerium at Darmstadt, Los Alamos records: it formed when dubnium-258 captured an electron, and it then decayed into other nuclides. At Dubna, its 0.3-second activity was tested against the relatively nonvolatile actinide trichlorides to show it was more volatile.