Atomic number 75

Rhenium

Re
+ phase
− phase

Shells Orbitals 4f 5d 6s

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75 electrons in 6 shells: 2, 8, 18, 32, 13, 2.

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

Category: Transition metal
Period: 6
Group: 7
Block: d
Standard atomic weight: 186.21(1) Da
Electron configuration: [Xe] 4f¹⁴ 5d⁵ 6s²
Phase at 25 °C: solid
Melting point: 3186 °C
Boiling point: 5596 °C
Density: 20.8 g/cm³
Electronegativity (Pauling): 1.9
Discovered: 1925, Walter Noddack, Ida Tacke and Otto Berg

Neighbours in the table

W Os

Rhenium was seen before it was held. In 1925 Walter Noddack, Ida Tacke and Otto Berg, German chemists, announced that x-ray spectroscopy had shown the element in platinum ore and columbite, Los Alamos and CIAAW record. Three years later Noddack and Berg worked through 660 kilograms of molybdenite, a molybdenum sulfide ore, for a single gram, Jefferson Lab’s account says. The name comes from rhenus, Latin for the river Rhine.

Rhenium is [Xe] 4f¹⁴ 5d⁵ 6s², or 2, 8, 18, 32, 13 and 2 by shell. In Chem1’s table the f-block slots in after the third group of the d-block, so a full 4f subshell is in place before the five 5d electrons. Those d electrons let transition metals take several valences. Rhenium’s oxidation states run from +7 down to −3 in Los Alamos’s list, and +7, +6 and +4 in Jefferson Lab’s. Each is a bookkeeping charge, the one the atom would carry were all its bonds ionic.

The metal is silvery white, and its melting point, 3186 °C, is exceeded among the elements only by those of tungsten and carbon, according to Los Alamos. In Chem1’s account, transition metals, which have valence-level d electrons, are generally stronger and melt higher. Annealed rhenium is very ductile, Los Alamos adds, and can be bent, coiled or rolled.

Where it is found

Rhenium never occurs free and forms no mineral of its own, according to Los Alamos, which puts it through the crust at about 0.001 parts per million. By Jefferson Lab’s figures, a kilogram of crust holds 7 × 10⁻⁴ milligrams and a litre of seawater 4 × 10⁻⁶ milligrams. Most of it lies with molybdenum in porphyry copper deposits, in the US Geological Survey’s account. Some molybdenum holds between 0.002 and 0.2 per cent rhenium, Los Alamos notes.

Three routes bring the metal to market, two as by-products of other refining. Roasting molybdenum concentrates from Arizona and Montana yields ammonium perrhenate, perrhenic acid and metal powder, the survey reports. In the sedimentary copper deposits of Armenia, Kazakhstan, Poland, Russia and Uzbekistan, rhenium-bearing residues are instead recovered at copper smelters. Hydrogen at high temperature reduces ammonium perrhenate to the metal, Los Alamos explains.

The third route is recycling. Scrapped turbine blades, superalloy scrap and spent catalysts gave about 25,000 kilograms of secondary rhenium worldwide in 2024, by industry estimates the survey reports. Mine output that year came to 62,000 kilograms per the survey, with Chile’s 29,000 kilograms the largest national share.

Why it matters

In the United States, superalloys for high-temperature turbine engine components take an estimated 80 per cent of rhenium’s end uses, the US Geological Survey reports. Superalloys are alloys made to keep their strength at high temperature. Petroleum-reforming catalysts take 15 per cent. In some nickel-base superalloys rhenium improves strength above 1,000 °C. The catalysts pair platinum with rhenium to turn petroleum into high-octane hydrocarbons for lead-free gasoline. One substitute, a catalyst built on iridium and tin, has reached commercial use.

Away from refineries, rhenium catalysts resist poisoning by nitrogen, sulfur and phosphorus and are used to hydrogenate fine chemicals, according to Los Alamos. Rhenium makes electrical contacts because it resists wear and withstands arc corrosion, Los Alamos says. Rhenium–tungsten thermocouples measure temperatures up to 2200 °C, and rhenium filaments serve in mass spectrographs and ion gauges. Alloys of rhenium and molybdenum become superconductors, carrying current without resistance, at about −263 °C.

One isotope keeps geological time. Rhenium-187 makes up 62.60 per cent of natural rhenium, in CIAAW’s figures, and beta-decays to osmium-187. Its half-life, the span in which half of any sample decays, is 41.6 billion years in the Atomic Mass Data Center’s data. That decay is the basis of rhenium–osmium dating, used on meteorites, gold deposits, copper-nickel deposits and rhenium-bearing ores.

Properties

Properties of rhenium 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	75
Standard atomic weight	186.21(1) Da	Da	IUPAC/CIAAW 2024
Melting point	3186 °C	°C	Los Alamos: 3186 °C
Boiling point	5596 °C	°C	PubChem: 5869 K
Density	20.8 g/cm³	g/cm³
Electronegativity (Pauling)	1.9
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁵
Phase at 25 °C	solid

Safety

Rhenium is usually sold as a powder, according to Los Alamos, and Haz-Map, an occupational health database, describes the powdered form as flammable. Company notifications under the Globally Harmonized System (GHS) class rhenium as a flammable solid, signal word Danger, in 63.9% of reports, and 34.9% find it meets no hazard criteria. Little is known about the metal’s toxicity, Los Alamos says. Rhenium’s full classification and precautions are set out in PubChem’s Laboratory Chemical Safety Summary for the element.

Questions

Is rhenium radioactive?

Natural rhenium is 37.40 per cent rhenium-185 and 62.60 per cent rhenium-187, in the figures of IUPAC's atomic-weights commission (CIAAW). Rhenium-187 does decay, but its half-life is 41.6 billion years. Two short-lived isotopes serve medicine, IUPAC notes: rhenium-186, made when rhenium-185 captures a neutron (the (n, γ) reaction), and rhenium-188. Rhenium-186 decays by two branches in the Atomic Mass Data Center's data, 92.53 per cent beta-minus and 7.47 per cent electron capture.

How much does rhenium cost?

Rhenium metal pellets averaged $1,370 per kilogram in 2024, the US Geological Survey estimates, 28 per cent more than the 2023 average of $1,070. Catalytic-grade ammonium perrhenate averaged $1,270 per kilogram, up 38 per cent from $920. World mine output held near 62,000 kilograms of rhenium content in 2024, against 62,600 in 2023, the survey adds.

What is the melting point of rhenium?

Rhenium melts at 3186 °C in PubChem's record, and among the elements only tungsten and carbon melt higher, according to Los Alamos. Its boiling point is 5596 °C in PubChem's record and 5630 °C by Los Alamos's figure. Annealed rhenium, heat-treated to soften it, stays ductile enough to bend, coil or roll, Los Alamos adds, and rhenium–tungsten thermocouples read temperatures up to 2200 °C.

Where does the United States get its rhenium?

Partly at home: roasting molybdenum concentrates from Arizona and Montana gave about 9,500 kilograms in 2024, the US Geological Survey estimates. Net imports covered about 65 per cent of the rhenium the country consumed. From 2020 to 2023 they came mainly from Chile (44 per cent), Canada (16), Germany (13) and Poland (10). The United States and Germany also lead in recycled rhenium, the survey adds.