Chemical element · Atomic number 27
Cobalt
Cobalt in the periodic table: atomic number 27, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Transition metal
solid
58.93319 u
Documented element sampleA documented sample of elemental cobalt, a silvery-gray metal.
Image credit: James St. John
Auto-oriented, limited to 1600 × 1200 pixels and re-encoded as WebP; the subject was not altered.
Atomic classification
Shell occupancy
Cobalt in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- L · n=2
- 8 electrons
- M · n=3
- 15 electrons
- N · n=4
- 2 electrons
- Electron configuration
- [Ar]4s2 3d7
- Electrons per shell
- 2 · 8 · 15 · 2
- Group
- 9
- Period
- 4
- Block
- D
- Element category
- Transition metal
Physical and chemical properties
- Atomic mass
- 58.93319 u
- Standard state
- solid
- Density
- 8.86 g/cm³
- Melting point
- 1,768 K
- Boiling point
- 3,200 K
- Electronegativity
- 1.88 (Pauling)
- First ionisation energy
- 7.881 eV
- Oxidation states
- +3, +2
- Discovery
- 1735
Safety and periodic classification
Safety
Safe handling cannot be inferred from Cobalt's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Cobalt is in period 4, group 9 and the D block. Its direct neighbours by atomic number are Iron and Nickel. The recorded Pauling electronegativity is 1.88. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.
Where Cobalt sits among the 118 elements
The table compares the reported values for Cobalt with every other element that carries the same value in the snapshot. A rank is not a judgement, it is orientation: it says how unusual this value is across the periodic table.
| Value | Cobalt | Position in the data set |
|---|---|---|
| Melting point | 1,768 K | Rank 30 of 103 elements with a reported value. Highest: Carbon. |
| Boiling point | 3,200 K | Rank 35 of 93 elements with a reported value. Highest: Rhenium. |
| Density | 8.86 g/cm³ | Rank 34 of 96 elements with a reported value. Highest: Osmium. |
| Electronegativity (Pauling) | 1.88 | Rank 40 of 95 elements with a reported value. Highest: Fluorine. |
| Ionisation energy | 7.881 eV | Rank 38 of 102 elements with a reported value. Highest: Helium. |
All values and ranks come from the PubChem Periodic Table snapshot, retrieved on 2026-07-15. Elements without a reported value are excluded, so the population differs per row.
The neighbours of Cobalt in the periodic table
- Place in the table
- Group 9, period 4, D block. Classified as transition metal, solid at standard conditions.
- Direct neighbours
- Atomic number 27. Preceded by Iron, followed by Nickel.
- Same group
- Same number of outer electrons, and therefore similar reactivity to Rhodium, Iridium, Meitnerium.
- Discovery
- Recorded in the snapshot as: 1735. Who, where and under what circumstances is not part of that record, so this page carries the sourced year and no discovery narrative.
- Oxidation states
- +3, +2. They follow from the electron configuration [Ar]4s2 3d7 and indicate which compounds to expect.
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