Co
Cobalt
Element 27 · Transition metal
Cobalt (Co)
Cobalt is a hard, magnetic, silvery-blue metal. It is a key ingredient in rechargeable batteries and heat-resistant superalloys.
- Transition metal
- Period 4
- Group 9
- d-block
- solid at room temperature
Key properties
- Atomic mass
- 58.9332
- u
- Electron configuration
- [Ar] 3d7 4s2
- Melting point
- 1,494.9 °C
- 1,768 K
- Boiling point
- 2,926.9 °C
- 3,200 K
- Density
- 8.86 g/cm³
- Electronegativity
- 1.88
- Pauling
- Atomic radius
- 192 pm
- van der Waals
- 1st ionisation energy
- 7.881 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about cobalt
- 01
Cobalt blue pigments have coloured glass and ceramics for thousands of years.
- 02
Vitamin B12 is built around a single cobalt atom.
- 03
Cobalt-60 is used to sterilise medical equipment and treat cancer.
Applications
What is cobalt used for?
- Lithium-ion battery cathodes
- Jet engine superalloys
- Blue pigments
- Radiotherapy (Co-60)
History
Discovery & name origin
Discovered by
Year
Where
Sweden
Name origin
German Kobold, “goblin” — miners blamed goblins for ores that gave off toxic fumes.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 27
- Atomic mass
- 58.9332 u
- Group
- 9
- Period
- 4
- Block
- d-block
- Electron configuration
- [Ar] 3d7 4s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d7
- Electrons per shell
- 2, 8, 15, 2
- Electronegativity (Pauling)
- 1.88
- Electron affinity
- 0.661 eV
- Atomic radius (van der Waals)
- 192 pm
- Stable isotopes
- 1
Oxidation states
Highlighted: common oxidation states (+3, +2).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st760.4
- 2nd1,648
- 3rd3,232
- 4th4,950
- 5th7,670
- 6th9,840
- 7th12,440
- 8th15,230
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Solid
- Melting point
- 1,768 K · 1,494.9 °C · 2,722.7 °F
- Boiling point
- 3,200 K · 2,926.9 °C · 5,300.3 °F
- Density
- 8.86 g/cm³
- Molar heat capacity
- 24.81 J/(mol·K)
- Appearance
- Hard lustrous grey metal
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Cobalt questions
What is Co on the periodic table?
Co is the symbol for cobalt, element 27 on the periodic table. It sits in group 9, period 4, in the transition metal category, and has an atomic mass of 58.9332.
What is the atomic number of cobalt?
Cobalt has atomic number 27, so every cobalt atom has 27 protons in its nucleus. Its symbol is Co and its atomic mass is 58.9332.
Who discovered cobalt?
Cobalt was discovered by Georg Brandt in 1735 (Sweden). The name comes from German Kobold, “goblin” — miners blamed goblins for ores that gave off toxic fumes.
What is cobalt used for?
Cobalt is used for: lithium-ion battery cathodes; jet engine superalloys; blue pigments; radiotherapy (Co-60).
Is cobalt a metal?
Yes. Cobalt is a transition metal, one of the metallic elements.
What is the electron configuration of cobalt?
The electron configuration of cobalt is [Ar] 3d7 4s2. Its 27 electrons are arranged in shells as 2, 8, 15, 2.