Rutherfordium

Rutherfordium, ₁₀₄Rf

Rutherfordium
Pronunciation	/ˌrʌðərˈfɔːrdiəm/ ( listen )​(RUDH-ər-FOR-dee-əm)
Mass number	[267]
Rutherfordium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Hf ↑ Rf ↓ (Upo) lawrencium ← rutherfordium → dubnium
Atomic number (Z)	104
Group	group 4
Period	period 7
Block	d-block
Element category	Transition metal
Electron configuration	[ Rn ] 5f14 6d2 7s2 [1] [2]
Electrons per shell	2, 8, 18, 32, 32, 10, 2
Physical properties
Phase at  STP	solid (predicted) [1] [2]
Melting point	2400  K ​(2100 °C,​3800 °F)(predicted) [1] [2]
Boiling point	5800 K​(5500 °C,​9900 °F)(predicted) [1] [2]
Density (near r.t.)	23.2 g/cm3(predicted) [1] [2] [3]
Atomic properties
Oxidation states	(+2), (+3), +4 [1] [2] [3] (parenthesized: prediction)
Ionization energies	1st: 580 kJ/mol 2nd: 1390 kJ/mol 3rd: 2300 kJ/mol (more)(all but first estimated) [2]
Atomic radius	empirical:150  pm (estimated) [2]
Covalent radius	157 pm(estimated) [1]
Other properties
Natural occurrence	synthetic
Crystal structure	​ hexagonal close-packed (hcp) (predicted) [4]
CAS Number	53850-36-5
History
Naming	after Ernest Rutherford
Discovery	Joint Institute for Nuclear Research and Lawrence Berkeley National Laboratory (1964, 1969)
Main isotopes of rutherfordium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 261Rf syn 70 s [5] >80% α 257No <15% ε 261Lr <10% SF 263Rf syn 15 min [5] <100% SF ~30% α 259No 265Rf syn 1.1 min [6] SF 266Rf syn 23 s? SF 267Rf syn 1.3 h [5] SF
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Rutherfordium is a synthetic chemical element with the symbol Rf and atomic number 104, named after New Zealand physicist Ernest Rutherford. As a synthetic element, it is not found in nature and can only be created in a laboratory. It is radioactive; the most stable known isotope, ²⁶⁷Rf, has a half-life of approximately 1.3 hours.

In the periodic table of the elements, it is a d-block element and the second of the fourth-row transition elements. It is a member of the 7th period and belongs to the group 4 elements. Chemistry experiments have confirmed that rutherfordium behaves as the heavier homologue to hafnium in group 4. The chemical properties of rutherfordium are characterized only partly. They compare well with the chemistry of the other group 4 elements, even though some calculations had indicated that the element might show significantly different properties due to relativistic effects.

In the 1960s, small amounts of rutherfordium were produced in the Joint Institute for Nuclear Research in the former Soviet Union and at Lawrence Berkeley National Laboratory in California. ^[7] The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) established rutherfordium as the official name for the element.

History

Discovery

Rutherfordium was reportedly first detected in 1964 at the Joint Institute of Nuclear Research at Dubna (then in the Soviet Union). Researchers there bombarded a plutonium-242 target with neon-22 ions and separated the reaction products by gradient thermochromatography after conversion to chlorides by interaction with ZrCl₄. The team identified spontaneous fission activity contained within a volatile chloride portraying eka-hafnium properties. Although a half-life was not accurately determined, later calculations indicated that the product was most likely rutherfordium-259 (abbreviated as ²⁵⁹Rf in standard notation): ^[8]

²⁴²
₉₄Pu
+ ²²
₁₀Ne
→ ^264−x
₁₀₄Rf
→ ^264−x
₁₀₄Rf
Cl₄

In 1969, researchers at the University of California, Berkeley conclusively synthesized the element by bombarding a californium-249 target with carbon-12 ions and measured the alpha decay of ²⁵⁷Rf, correlated with the daughter decay of nobelium-253: ^[9]

²⁴⁹
₉₈Cf
+ ¹²
₆C
→ ²⁵⁷
₁₀₄Rf
+ 4
n

The American synthesis was independently confirmed in 1973 and secured the identification of rutherfordium as the parent by the observation of K-alpha X-rays in the elemental signature of the ²⁵⁷Rf decay product, nobelium-253. ^[10]

Naming controversy

Main article: Transfermium Wars

Element 104 was eventually named after Ernest Rutherford

The Russian scientists proposed the name kurchatovium and the American scientists suggested the name rutherfordium for the new element. ^[11] In 1992, the IUPAC/IUPAP Transfermium Working Group (TWG) assessed the claims of discovery and concluded that both teams provided contemporaneous evidence to the synthesis of element 104 and that credit should be shared between the two groups. ^[8]

The American group wrote a scathing response to the findings of the TWG, stating that they had given too much emphasis on the results from the Dubna group. In particular they pointed out that the Russian group had altered the details of their claims several times over a period of 20 years, a fact that the Russian team does not deny. They also stressed that the TWG had given too much credence to the chemistry experiments performed by the Russians and accused the TWG of not having appropriately qualified personnel on the committee. The TWG responded by saying that this was not the case and having assessed each point raised by the American group said that they found no reason to alter their conclusion regarding priority of discovery. ^[12] The IUPAC finally used the name suggested by the American team (rutherfordium) which may in some way reflect a change of opinion. ^[13]

As a consequence of the initial competing claims of discovery, an element naming controversy arose. Since the Soviets claimed to have first detected the new element they suggested the name kurchatovium (Ku) in honor of Igor Kurchatov (1903–1960), former head of Soviet nuclear research. This name had been used in books of the Soviet Bloc as the official name of the element. The Americans, however, proposed rutherfordium (Rf) for the new element to honor Ernest Rutherford, who is known as the "father" of nuclear physics. The International Union of Pure and Applied Chemistry (IUPAC) adopted unnilquadium (Unq) as a temporary, systematic element name, derived from the Latin names for digits 1, 0, and 4. In 1994, IUPAC suggested the name dubnium (Db) to be used since rutherfordium was suggested for element 106 and IUPAC felt that the Dubna team should be recognized for their contributions. However, there was still a dispute over the names of elements 104–107. In 1997 the teams involved resolved the dispute and adopted the current name rutherfordium. The name dubnium was given to element 105 at the same time. ^[13]

Isotopes

Isotope half-lives and discovery years

Isotope	Half-life [5]	Decay mode [5]	Discovery year	Reaction
253Rf	48 μs	α, SF	1994	204Pb(50Ti,n) [14]
254Rf	23 μs	SF	1994	206Pb(50Ti,2n) [14]
255Rf	2.3 s	ε?, α, SF	1974	207Pb(50Ti,2n) [15]
256Rf	6.4 ms	α, SF	1974	208Pb(50Ti,2n) [15]
257Rf	4.7 s	ε, α, SF	1969	249Cf(12C,4n) [9]
257mRf	4.1 s	ε, α, SF	1969	249Cf(12C,4n) [9]
258Rf	14.7 ms	α, SF	1969	249Cf(13C,4n) [9]
259Rf	3.2 s	α, SF	1969	249Cf(13C,3n) [9]
259mRf	2.5 s	ε	1969	249Cf(13C,3n) [9]
260Rf	21 ms	α, SF	1969	248Cm(16O,4n) [8]
261Rf	78 s	α, SF	1970	248Cm(18O,5n) [16]
261mRf	4 s	ε, α, SF	2001	244Pu(22Ne,5n) [17]
262Rf	2.3 s	α, SF	1996	244Pu(22Ne,4n) [18]
263Rf	15 min	α, SF	1999	263Db( e− , ν e) [19]
263mRf ?	8 s	α, SF	1999	263Db( e− , ν e) [19]
265Rf	1.1 min [6]	SF	2010	269Sg(—,α) [20]
266Rf	23 s?	SF	2007?	266Db( e− , ν e)? [21] [22]
267Rf	1.3 h	SF	2004	271Sg(—,α) [23]
268Rf	1.4 s?	SF	2004?	268Db( e− , ν e)? [22] [24]
270Rf	20 ms? [25]	SF	2010?	270Db( e− , ν e)? [26]

Main article: Isotopes of rutherfordium

Rutherfordium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Sixteen different isotopes have been reported with atomic masses from 253 to 270 (with the exceptions of 264 and 269). Most of these decay predominantly through spontaneous fission pathways. ^{[5] [27]}

Stability and half-lives

Out of isotopes whose half-lives are known, the lighter isotopes usually have shorter half-lives; half-lives of under 50 μs for ²⁵³Rf and ²⁵⁴Rf were observed. ²⁵⁶Rf, ²⁵⁸Rf, ²⁶⁰Rf are more stable at around 10 ms, ²⁵⁵Rf, ²⁵⁷Rf, ²⁵⁹Rf, and ²⁶²Rf live between 1 and 5 seconds, and ²⁶¹Rf, ²⁶⁵Rf, and ²⁶³Rf are more stable, at around 1.1, 1.5, and 10 minutes respectively. The heaviest isotopes are the most stable, with ²⁶⁷Rf having a measured half-life of about 1.3 hours. ^[5]

The lightest isotopes were synthesized by direct fusion between two lighter nuclei and as decay products. The heaviest isotope produced by direct fusion is ²⁶²Rf; heavier isotopes have only been observed as decay products of elements with larger atomic numbers, of which only ²⁶⁷Rf has been confirmed. The heavy isotopes ²⁶⁶Rf and ²⁶⁸Rf have also been observed as electron capture daughters of the dubnium isotopes ²⁶⁶Db and ²⁶⁸Db, but have short half-lives to spontaneous fission. It seems likely that the same is true of ²⁷⁰Rf, a likely daughter of ²⁷⁰Db. ^[26]

In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of ²⁹³Og. ^[28] These parent nuclei were reported to have successively emitted seven alpha particles to form ²⁶⁵Rf nuclei, but their claim was retracted in 2001. ^[29] This isotope was later discovered in 2010 as the final product in the decay chain of ²⁸⁵Fl. ^{[6] [20]}

Predicted properties

Chemical

Rutherfordium is the first transactinide element and the second member of the 6d series of transition metals. Calculations on its ionization potentials, atomic radius, as well as radii, orbital energies, and ground levels of its ionized states are similar to that of hafnium and very different from that of lead. Therefore, it was concluded that rutherfordium's basic properties will resemble those of other group 4 elements, below titanium, zirconium, and hafnium. ^{[19] [30]} Some of its properties were determined by gas-phase experiments and aqueous chemistry. The oxidation state +4 is the only stable state for the latter two elements and therefore rutherfordium should also exhibit a stable +4 state. ^[30] In addition, rutherfordium is also expected to be able to form a less stable +3 state. ^[2] The standard reduction potential of the Rf⁴⁺/Rf couple is predicted to be higher than −1.7 V. ^[3]

Initial predictions of the chemical properties of rutherfordium were based on calculations which indicated that the relativistic effects on the electron shell might be strong enough that the 7p orbitals would have a lower energy level than the 6d orbitals, giving it a valence electron configuration of 6d¹ 7s² 7p¹ or even 7s² 7p², therefore making the element behave more like lead than hafnium. With better calculation methods and experimental studies of the chemical properties of rutherfordium compounds it could be shown that this does not happen and that rutherfordium instead behaves like the rest of the group 4 elements. ^{[2] [30]} Later it was shown in ab initio calculations with the high level of accuracy ^{[31] [32] [33]} that the Rf atom has the ground state with the 6d² 7s² valence configuration and the low-lying excited 6d¹ 7s² 7p¹ state with the excitation energy of only 0.3÷0.5 eV.

In an analogous manner to zirconium and hafnium, rutherfordium is projected to form a very stable, refractory oxide, RfO₂. It reacts with halogens to form tetrahalides, RfX₄, which hydrolyze on contact with water to form oxyhalides RfOX₂. The tetrahalides are volatile solids existing as monomeric tetrahedral molecules in the vapor phase. ^[30]

In the aqueous phase, the Rf⁴⁺ ion hydrolyzes less than titanium(IV) and to a similar extent as zirconium and hafnium, thus resulting in the RfO²⁺ ion. Treatment of the halides with halide ions promotes the formation of complex ions. The use of chloride and bromide ions produces the hexahalide complexes RfCl²⁻
₆ and RfBr²⁻
₆. For the fluoride complexes, zirconium and hafnium tend to form hepta- and octa- complexes. Thus, for the larger rutherfordium ion, the complexes RfF²⁻
₆, RfF³⁻
₇ and RfF⁴⁻
₈ are possible. ^[30]

Physical and atomic

Rutherfordium is expected to be a solid under normal conditions and assume a hexagonal close-packed crystal structure (^c/_a = 1.61), similar to its lighter congener hafnium. ^[4] It should be a very heavy metal with a density of around 23.2 g/cm³; in comparison, the densest known element that has had its density measured, osmium, has a density of 22.61 g/cm³. This results from rutherfordium's high atomic weight, the lanthanide and actinide contractions, and relativistic effects, although production of enough rutherfordium to measure this quantity would be impractical, and the sample would quickly decay. The atomic radius for rutherfordium is expected to be around 150  pm. Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Rf⁺ and Rf²⁺ ions are predicted to give up 6d electrons instead of 7s electrons, which is the opposite of the behavior of its lighter homologues. ^[2] When under high pressure (variously calculated as 72 or ~50 GPa), rutherfordium is expected to transition to a body-centered cubic crystal structure; hafnium transforms to this structure at 71±1 GPa, but has an intermediate ω structure that it transforms to at 38±8 GPa that is lacking for rutherfordium. ^[34]

Experimental chemistry

Summary of compounds and complex ions

Formula	Names
RfCl4	rutherfordium tetrachloride, rutherfordium(IV) chloride
RfBr4	rutherfordium tetrabromide, rutherfordium(IV) bromide
RfOCl2	rutherfordium oxychloride, rutherfordyl(IV) chloride, rutherfordium(IV) dichloride oxide
[RfCl6]2−	hexachlororutherfordate(IV)
[RfF6]2−	hexafluororutherfordate(IV)
K2[RfCl6]	potassium hexachlororutherfordate(IV)

Gas phase

The tetrahedral structure of the RfCl₄ molecule

Early work on the study of the chemistry of rutherfordium focused on gas thermochromatography and measurement of relative deposition temperature adsorption curves. The initial work was carried out at Dubna in an attempt to reaffirm their discovery of the element. Recent work is more reliable regarding the identification of the parent rutherfordium radioisotopes. The isotope ^261mRf has been used for these studies, ^[30] though the long-lived isotope ²⁶⁷Rf (produced in the decay chains of ²⁹¹Lv, ²⁸⁷Fl, and ²⁸³Cn) may be advantageous for future experiments. ^[35] The experiments relied on the expectation that rutherfordium would begin the new 6d series of elements and should therefore form a volatile tetrachloride due to the tetrahedral nature of the molecule. ^{[30] [36] [37]} Rutherfordium(IV) chloride is more volatile than its lighter homologue hafnium(IV) chloride (HfCl₄) because its bonds are more covalent. ^[2]

A series of experiments confirmed that rutherfordium behaves as a typical member of group 4, forming a tetravalent chloride (RfCl₄) and bromide (RfBr₄) as well as an oxychloride (RfOCl₂). A decreased volatility was observed for RfCl
_⁴ when potassium chloride is provided as the solid phase instead of gas, highly indicative of the formation of nonvolatile K
_²RfCl
_⁶ mixed salt. ^{[19] [30] [38]}

Aqueous phase

Rutherfordium is expected to have the electron configuration [Rn]5f¹⁴ 6d² 7s² and therefore behave as the heavier homologue of hafnium in group 4 of the periodic table. It should therefore readily form a hydrated Rf⁴⁺ ion in strong acid solution and should readily form complexes in hydrochloric acid, hydrobromic or hydrofluoric acid solutions. ^[30]

The most conclusive aqueous chemistry studies of rutherfordium have been performed by the Japanese team at Japan Atomic Energy Research Institute using the isotope ^261mRf. Extraction experiments from hydrochloric acid solutions using isotopes of rutherfordium, hafnium, zirconium, as well as the pseudo-group 4 element thorium have proved a non-actinide behavior for rutherfordium. A comparison with its lighter homologues placed rutherfordium firmly in group 4 and indicated the formation of a hexachlororutherfordate complex in chloride solutions, in a manner similar to hafnium and zirconium. ^{[30] [39]}

^261m
Rf⁴⁺
+ 6 Cl⁻
→ [^261mRfCl
_⁶]²⁻

Very similar results were observed in hydrofluoric acid solutions. Differences in the extraction curves were interpreted as a weaker affinity for fluoride ion and the formation of the hexafluororutherfordate ion, whereas hafnium and zirconium ions complex seven or eight fluoride ions at the concentrations used: ^[30]

^261m
Rf⁴⁺
+ 6 F⁻
→ [^261mRfF
_⁶]²⁻

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External links

• Rutherfordium at The Periodic Table of Videos (University of Nottingham)
• WebElements.com – Rutherfordium