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Bh

Bohrium

properties predicted

Bohrium (Bh) is a transition metal with atomic number 107. It has no stable isotope and no characteristic isotopic composition on Earth, so it has no standard atomic weight. CIAAW lists bohrium-270 and bohrium-274 as its longest-lived isotopes, and the mass number used here is 270. Its electron configuration is predicted to be [Rn] 5f14 6d5 7s2.

Bohrium key data

Symbol Bh
Atomic number 107
Mass number (one of its longest-lived isotopes) 270
Protons 107
Neutrons (bohrium-270) 163
Electrons (neutral atom) 107
Category Transition metal
Period 7
Group 7
Block d-block
Noble gas notation [Rn] 5f14 6d5 7s2
Full electron configuration 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

Mass number: IUPAC CIAAW radioactive elements, from NUBASE2020.

The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.

Properties of bohrium

From PubChem, the US National Institutes of Health. Public domain. Most properties of this element are predicted, because only a few atoms have ever been made. The discovery year is the year bohrium was first conclusively identified, from Wikipedia’s timeline of chemical element discoveries, in place of PubChem’s 1976.

Predicted state at room temperature Solid
Predicted oxidation states +7, +5, +4, +3
Discovered 1981

Bohrium electron configuration

The full electron configuration of bohrium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 6d5 7s2. With the noble-gas core collapsed it is [Rn] 5f14 6d5 7s2, and the outermost subshell is 7s2.

Bohr model of bohrium (Bh): a nucleus and seven shells holding 2, 8, 18, 32, 32, 13 and 2 electrons from the inside out.
Bohr model of bohrium (Bh). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.
Orbital box diagram of bohrium (Bh), [Rn] 5f14 6d5 7s2, with the radon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing five unpaired electrons, in 6d.
Orbital diagram of bohrium (Bh). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one bohrium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

  1. one atom = 270 / (6.02214076 × 10²³)
  2. = 4.4835 × 10⁻²² g

Atoms in one gram

  1. atoms per gram = 6.02214076 × 10²³ / 270
  2. = 2.2304 × 10²¹ atoms

Bohrium has no standard atomic weight, because it has neither a stable isotope nor a characteristic isotopic composition on Earth. The figure used above is the mass number of bohrium-270, so treat these as nominal.

Bohrium on the periodic table

Bohrium is in period 7, group 7, in the d-block.

The other elements of group 7 are manganese, technetium and rhenium.

The rest of period 7

Work with bohrium