Cobalt (Co)
Element 27 · Transition metal · atomic mass 58.933 u · group 9, period 4
Electron shells: 2, 8, 15, 2
Cobalt gives glass and ceramics their classic deep blue and holds its strength at high temperature. It is also a vitamin B12 component and a critical battery material.
Miners named it after goblins, blaming them for ore that poisoned smelters and yielded no copper.
- Atomic number
- 27
- Atomic mass
- 58.933 u
- Electron configuration
- [Ar] 4s² 3d⁷
- Group · period · block
- 9 · 4 · d
- Oxidation states
- +2, +3
- Electronegativity
- 1.88 (Pauling)
- Melting point
- 1,495 °C
- Boiling point
- 2,927 °C
- Density
- 8.86 g/cm³
- State at 20 °C
- Solid
- Appearance
- Hard, lustrous silvery-blue metal
- Discovered
- Georg Brandt, 1735
27 protons, and 27 electrons when neutral
IUPAC standard atomic weight
Cobalt group
What Cobalt is used for
- Lithium-ion battery cathodes
- Superalloys for jet engines
- Blue pigments in glass and ceramics
- Cutting tools and magnets
Atomic structure of Cobalt
A neutral cobalt atom has 27 protons and 27 electrons. Its most common isotope carries about 32 neutrons, which is where the mass number 59 comes from. Change the neutron count and you have a different isotope of cobalt; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 15, 2. In orbital notation that is [Ar] 4s² 3d⁷. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Cobalt's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Cobalt sits in the periodic table
Discovery and naming
Cobalt was discovered by Georg Brandt in 1735. Its name comes from German kobold, "goblin".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Cobalt?
The standard atomic weight of Cobalt is 58.933 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Cobalt have?
Cobalt has 27 protons, because the atomic number is the proton count and that is what makes an atom Cobalt at all. A neutral Cobalt atom has the same number of electrons, 27. The neutron count varies by isotope; the most common one has about 32, since 59 − 27 = 32.
What is the electron configuration of Cobalt?
The electron configuration of Cobalt is [Ar] 4s² 3d⁷. Its electrons are arranged 2, 8, 15, 2 across 4 shells.
Is Cobalt a metal?
Yes. Cobalt is classified as a transition metal, on the metallic side of the table.
What group and period is Cobalt in?
Cobalt is in group 9 (the cobalt group), period 4, in the d-block. The group is its column and the period is its row.
What is the charge of Cobalt?
Cobalt most commonly forms a 2+ or 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Cobalt?
Cobalt melts at 1,495 °C and boils at 2,927 °C. That puts it in the solids at everyday temperatures.
What is Cobalt used for?
Lithium-ion battery cathodes, Superalloys for jet engines, Blue pigments in glass and ceramics, Cutting tools and magnets. Cobalt gives glass and ceramics their classic deep blue and holds its strength at high temperature.
Who discovered Cobalt, and where does its name come from?
Cobalt (Co) was discovered by Georg Brandt in 1735. The name comes from German kobold, "goblin".