Bohrium (Bh)
Bohrium (Bh) is a transition metal with atomic number 107; its most stable known isotope has mass number 270. Only a few atoms have ever been made, so its bulk properties are predictions.
Bohrium key facts
Bohrium at a glance
Identity
| Symbol | Bh |
|---|---|
| Atomic number (Z) | 107 |
| Atomic weight | [270] mass number of the most stable isotope |
| Category | Transition metal |
| Group | 7 |
| Period | 7 |
| Block | d-block |
| CAS number | 54037-14-8 |
Atomic properties
| Electron configuration | [Rn] 5f14 6d5 7s2 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 6d5 7s2 |
|---|---|
| Electrons per shell | 2, 8, 18, 32, 32, 13, 2 |
| First ionisation energy | 7.7 eV (742.9 kJ/mol) 2nd: 17.5 eV · 3rd: 26.7 eV |
| Covalent radius | 141 pm |
Physical properties
| State at 25 °C | Unknown (predicted solid) |
|---|---|
| Density | 37.1 g/cm³ (predicted) |
Isotopes & abundance
| Natural occurrence | Synthetic |
|---|---|
| Radioactive | Yes |
| Most stable isotope | 270Bh — half-life 3.8 min |
| Known isotopes | 19 |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Bohrium electron configuration
Bohrium has 107 electrons. Written in short form, its ground-state configuration is [Rn] 5f14 6d5 7s2 — the electrons of the noble gas radon, plus 5f14 6d5 7s2.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 6d5 7s2.
Discovery and name
1981 — Peter Armbruster and Gottfried Münzenberg (GSI) · Germany (Darmstadt).
Niels Bohr.
Known for
Its chemistry was first studied with just six atoms; it behaves like rhenium.
Isotopes of bohrium
Bohrium has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:
| Isotope | Protons | Neutrons | Half-life |
|---|---|---|---|
| 270Bh | 107 | 163 | 3.8 min |
19 isotopes of bohrium are known in our data set (half-lives as published in nuclear data tables).
Bohrium 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.) | — |