Cobalt Element Facts

The chemical element cobalt is classed as a transition metal. It was discovered in 1735 by George Brandt.

Cobalt. Photo by Ben Mills

Data Zone

Classification: Cobalt is a transition metal
Color: bluish-white
Atomic weight: 58.9332
State: solid
Melting point: 1495 oC, 1768 K
Boiling point: 2930 oC, 3203 K
Electrons: 27
Protons: 27
Neutrons in most abundant isotope: 32
Electron shells: 2,8,15,2
Electron configuration: [Ar] 3d7 4s2
Density @ 20oC: 8.90 g/cm3
Show more: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities
Atomic volume: 6.7 cm3/mol
Structure: hcp: hexagonal close pkd
Hardness: 5.0 mohs
Specific heat capacity 0.42 J g-1 K-1
Heat of fusion 16.190 kJ mol-1
Heat of atomization 426 kJ mol-1
Heat of vaporization 373.3 kJ mol-1
1st ionization energy 758.4 kJ mol-1
2nd ionization energy 1646 kJ mol-1
3rd ionization energy 3232.2 kJ mol-1
Electron affinity 63.8 kJ mol-1
Minimum oxidation number -1
Min. common oxidation no. 0
Maximum oxidation number 5
Max. common oxidation no. 3
Electronegativity (Pauling Scale) 1.88
Polarizability volume 7.5 Å3
Reaction with air mild, w/ht ? Co3O4
Reaction with 15 M HNO3 vigorous, ? Co(NO3)2, NOx
Reaction with 6 M HCl mild, ? H2, CoCl2
Reaction with 6 M NaOH
Oxide(s) CoO, Co3O4
Hydride(s) None
Chloride(s) CoCl2
Atomic radius 135 pm
Ionic radius (1+ ion)
Ionic radius (2+ ion) 83.8 pm
Ionic radius (3+ ion) 71.8 pm
Ionic radius (1- ion)
Ionic radius (2- ion)
Ionic radius (3- ion)
Thermal conductivity 100 W m-1 K-1
Electrical conductivity 17.9 x 106 S m-1
Freezing/Melting point: 1495 oC, 1768 K

Discovery of Cobalt

Since ancient times cobalt compounds have been used to produce blue glass and ceramics.

The element was first isolated by Swedish chemist George Brandt in 1735. He showed it was the presence of the element cobalt that caused the blue color in glass, not bismuth as previously thought.

In about 1741 he wrote, “As there are six kinds of metals, so I have also shown with reliable experiments… that there are also six kinds of half-metals: a new half-metal, namely cobalt regulus in addition to mercury, bismuth, zinc, and the reguluses of antimony and arsenic.”

The word cobalt is derived from the German ‘kobold’, meaning goblin or elf.

Adding HCl shifts the equilibrium and color of a cobalt chloride solution. HCl added to the pink colored Co2+ solution results in the formation of a blue colored solution of CoCl42- ions. The reaction is reversible and the colors can switch back and forth when the Cl concentration changes.

Cobalt's electron shells

Cobalt’s electron shells

Appearance and Characteristics

Harmful effects:

Cobalt and its compounds are considered to be slightly toxic by skin contact and moderately toxic by ingestion.


Cobalt is a bluish-white, lustrous, hard, brittle metal. It is ferromagnetic.

The metal is active chemically, forming many compounds. Cobalt stays magnetic to the highest temperature of all the magnetic elements (it has a Curie point of 1121oC).

Uses of Cobalt

Cobalt is used in alloys for aircraft engine parts and in alloys with corrosion/wear resistant uses.

Cobalt is widely used in batteries and in electroplating.

Cobalt salts are used to impart blue and green colors in glass and ceramics.

Radioactive 60Co is used in the treatment of cancer.

Cobalt is essential to many living creatures and is a component of vitamin B12.

Cobalt is also used in samarium-cobalt permanent magnets. These are used in guitar pickups and high speed motors.

Abundance and Isotopes

Abundance earth’s crust: 25 parts per million by weight, 8 parts per million by moles

Abundance solar system: 4 parts per million by weight, 0.7 parts per million by moles

Cost, pure: $21 per 100g

Cost, bulk: $4.40 per 100g

Source: Cobalt is not found as a free element in nature. It is found in mineral ores. The main ores of cobalt are cobaltite (CoAsS), erythrite (hydrated arsenate of cobalt), glaucodot (Co,Fe)AsS, and skutterudite (Co,Ni)As3. Cobalt is generally produced as a by-product of nickel and copper mining.

Isotopes: Cobalt has 22 isotopes whose half-lives are known, with mass numbers 50 to 72. Naturally occurring cobalt consists of its one stable isotope, 59Co.

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  1. alejandra nava says:

    thank you so much for having all this good information, i need for a project and thank you for having the mla citation already done, it takes me a long time to find the citation

  2. thanks for the good info. But i still have 1 ? why does Co represent or symbolize cobalt?

    • CObalt, Co? I’m pretty sure that “Co” doesn’t really symbolise or represent anything other than the first two letters

  3. What is the atomic radius of Cobalt??

    • Hi Rachel,

      It’s 135 pm (picometers)

      You can see all the data in the data zone near the top of this page. For the radius you need to click on the part that says:

      “Show more: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities” 🙂

  4. This site is really helpful but I have a question: What does cobalt react with and what are the reactions?

    • Hi Kimmee, Cobalt can take part in a lot of reactions. We list some of these in the Data Zone near the top of this page. Scroll up to the Data Zone and click on “Show more: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities”. You’ll find its reactions with air (oxygen), nitric acid, hydrochloric acid, and sodium hydroxide (no reaction).

  5. what is the freezing and melting point of cobalt?

  6. Love this website

  7. What kinds of bonds does cobalt make with other elements? Like ionic or covalent?

  8. What is the freezing point of cobalt? It gives the boiling and melting point but not the freezing point…