Cobalt
Atomic Data
| Atomic Number | 27 |
| Symbol | Co |
| Atomic Weight | 58.933 u |
| Density (STP) | 8.9 g/cm³ |
| Melting Point | 1494.85 °C (1768 K) |
| Boiling Point | 2926.85 °C (3200 K) |
| Electronegativity | 1.88 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d7 4s2 |
| Oxidation States | +2, +3 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 4 / 9 |
| CAS Number | 7440-48-4 |
Electron Configuration
[Ar] 3d7 4s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 7 | 25 |
| N | 4 | 4s | 2 | 27 |
| Total | 27 | 27 | ||
Isotopes of Cobalt
Cobalt is monoisotopic: ⁵⁹Co is its only naturally occurring stable isotope, accounting for 100% of all natural Cobalt.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Cobalt-59 | ⁵⁹Co | 27 | 32 | 100 | Stable |
Abundance & Occurrence
Cobalt is present in Earth's crust at approximately 25 ppm by mass and at approximately 3 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Cobalt dust and fume: hard metal disease: Inhalation of cobalt dust or cobalt-tungsten carbide (hard metal) dust causes hard metal lung disease, a serious occupational interstitial pneumonia; cobalt is classified as a Group 2A probable human carcinogen (IARC).
- Skin sensitisation: Cobalt is one of the most common causes of occupational allergic contact dermatitis, particularly among workers in the hard metal, ceramics, and cement industries.
- Cobalt-60 radiation: The radioisotope Co-60 is a powerful gamma emitter widely used in radiotherapy and industrial radiography; improper handling or orphaned sources pose serious radiation hazards.
- Systemic toxicity: Excessive cobalt absorption (as occurred with cobalt-contaminated beer in the 1960s) causes cardiomyopathy, thyroid dysfunction, and neurological effects.
Cobalt in the Real World
Real-World Uses
- Rechargeable battery cathodes: Lithium cobalt oxide (LiCoO₂) and other cobalt-containing cathode materials power lithium-ion batteries in smartphones, laptops, and electric vehicles; cobalt provides high energy density and structural stability.
- Superalloys for jet engines: Cobalt-based superalloys (Stellite, Haynes alloys) and cobalt additions to nickel superalloys maintain strength and oxidation resistance at turbine inlet temperatures exceeding 1000 °C.
- Hard metal cutting tools: Cemented tungsten carbide tooling is bound together by 5–15% cobalt metal binder; cobalt provides the ductility and toughness that prevents brittle fracture of the carbide during machining.
- Permanent magnets: Samarium-cobalt (SmCo) and aluminium-nickel-cobalt (Alnico) magnets retain their magnetism at elevated temperatures, used in sensors, motors, and aerospace applications where Nd-Fe-B magnets are too susceptible to heat.
- Radiation therapy: Cobalt-60 (t½ = 5.27 yr) emits high-energy gamma rays used in teletherapy units to treat cancers, particularly in lower-resource settings where linear accelerators are unavailable.
- Blue pigments and glazes: Cobalt aluminate (cobalt blue) and cobalt silicate (smalt) are heat-stable ceramic, glass, and artists' pigments that have coloured pottery, tiles, and paintings deep blue since antiquity.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is cobalt used for?
Cobalt is used in lithium-ion batteries: it is a key component of the cathode in batteries that power smartphones, laptops, and electric vehicles. Cobalt is also used to make high-temperature superalloys for jet turbine blades, in hard cutting tools (cemented carbides), and as a blue pigment in glass, ceramics, and paint that has been prized since antiquity.
Is cobalt radioactive?
Natural cobalt consists entirely of the stable isotope Co-59, so cobalt metal is not radioactive. However, cobalt-60, a synthetic isotope produced in nuclear reactors, is intensely radioactive and widely used in medicine for cancer radiation therapy and in industry for gamma-ray imaging of welds and structural components.
How was cobalt discovered?
Cobalt was identified as a distinct element in 1735 by Swedish chemist Georg Brandt, making it the first metal to be discovered in historical times (rather than antiquity). Miners in the Ore Mountains of central Europe had long encountered cobalt ores, which they called 'kobold' ores, blaming troublesome gnomes when the ore produced no useful metal: it only yielded toxic arsenic fumes.
What is the cobalt supply chain concern?
More than 70% of the world's cobalt is mined in the Democratic Republic of Congo, and a significant portion comes from artisanal small-scale mines with documented human rights issues including child labour. This geographic and ethical concentration has driven major battery manufacturers to develop cobalt-reduced or cobalt-free cathode chemistries.