Rhenium (Re)
Rhenium (Re) is a transition metal with atomic number 75 and a standard atomic weight of 186.21. At room temperature it is a solid that melts at 3,185 °C and boils at 5,590 °C.
Rhenium key facts
Rhenium at a glance
Identity
| Symbol | Re |
|---|---|
| Atomic number (Z) | 75 |
| Atomic weight | 186.21 ± 0.01 (CIAAW 2024) |
| Category | Transition metal |
| Group | 7 |
| Period | 6 |
| Block | d-block |
| CAS number | 7440-15-5 |
Atomic properties
| Electron configuration | [Xe] 4f14 5d5 6s2 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d5 6s2 |
|---|---|
| Electrons per shell | 2, 8, 18, 32, 13, 2 |
| Oxidation states | +4 Less common: -3, -1, 0, +1, +2, +3, +5, +6, +7 |
| Electronegativity (Pauling) | 1.9 |
| First ionisation energy | 7.833 eV (755.8 kJ/mol) 2nd: 16.6 eV · 3rd: 27 eV |
| Electron affinity | 0.15 eV |
| Atomic radius (empirical) | 135 pm |
| Covalent radius | 131 pm |
| Van der Waals radius | 216 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 3,185 °C · 5,765 °F · 3,458.15 K |
| Boiling point | 5,590 °C · 10,094 °F · 5,863.15 K |
| Density | 20.8 g/cm³ |
| Specific heat capacity | 0.137 J/(g·K) |
| Thermal conductivity | 48 W/(m·K) |
| Crystal structure | Hexagonal |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 187Re 62.6% (radioactive), 185Re 37.4% |
| Stable isotopes | 1 |
| Known isotopes | 41 |
| Abundance in Earth's crust | 0.0007 mg/kg |
| Abundance in seawater | 0.000004 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Rhenium electron configuration
Rhenium has 75 electrons. Written in short form, its ground-state configuration is [Xe] 4f14 5d5 6s2 — the electrons of the noble gas xenon, plus 4f14 5d5 6s2.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d5 6s2.
Discovery and name
1925 — Walter Noddack, Ida Tacke (Noddack) and Otto Berg · Germany.
Latin Rhenus, the river Rhine.
Known for
One of the rarest elements. Used in nickel superalloys for jet-engine turbine blades and in petroleum-reforming catalysts.
Isotopes of rhenium
Naturally occurring rhenium is a mix of 2 isotopes. Each has 75 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 187Re | 75 | 112 | 62.6% | radioactive · half-life 41.6 billion years |
| 185Re | 75 | 110 | 37.4% | stable |
41 isotopes of rhenium are known in our data set (half-lives as published in nuclear data tables).
Rhenium compared with group 7
The other elements in group 7, from top to bottom of the table:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Manganese | 25 | 54.938 | 1,246 °C | 2,061 °C | 7.3 g/cm³ | 1.55 |
| Technetium | 43 | [97] | 2,157 °C | 4,262 °C | 11 g/cm³ | 1.9 |
| Rhenium | 75 | 186.21 | 3,185 °C | 5,590 °C | 20.8 g/cm³ | 1.9 |
| Bohrium | 107 | [270] | — | — | 37.1 g/cm³ (pred.) | — |