Cobalt (Co)
Transition metal
Cobalt gives us the intense blue of classic glass and ceramics, super-tough jet-engine alloys, and a large share of the cathodes in lithium-ion batteries. It is also the metal at the centre of vitamin B12.
Position on the periodic table
Atomic properties
| Atomic number | 27 |
|---|---|
| Atomic mass | 58.9332 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d7 |
| Noble gas shorthand | [Ar] 3d7 4s2 |
| Electrons per shell | 2, 8, 15, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +2, +3 |
| Electronegativity (Pauling) | 1.88 |
| Covalent radius (approx.) | 126 pm |
| First ionization energy | 760.4 kJ/mol |
| Electron affinity | 63.9 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 8.9 g/cm³ |
| Melting point | 1494.8 °C (1768 K) |
| Boiling point | 2926.8 °C (3200 K) |
| Appearance | hard lustrous gray metal |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of cobalt
Cobalt's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d7, usually shortened to [Ar] 3d7 4s2. Its electrons occupy 4 shells (2, 8, 15, 2), placing it in period 4 of the d-block. Explore it interactively in the electron configuration calculator.
Uses of cobalt
- Lithium-ion battery cathodes
- Superalloys for jet turbines
- Cobalt blue pigments in glass and ceramics
- Hard cutting tools and magnets
Biological role: Essential in trace amounts as the core atom of vitamin B12.
Occurrence: Mostly obtained as a by-product of copper and nickel mining.
Common compounds of cobalt
CoO
Cobalt(II) oxide
CoCl2
Cobalt(II) chloride
History and discovery
Discovered: 1735 — Georg Brandt. Name origin: From German Kobold, a goblin blamed for troublesome ores.
Georg Brandt identified cobalt around 1735 — the first metal discovered since ancient times.
Safety notes
Cobalt dust and soluble salts are harmful with chronic exposure; trace dietary cobalt (in B12) is essential.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Cobalt
1. What is the chemical symbol of Cobalt?
2. What is the atomic number of Cobalt?
3. Which category does Cobalt belong to?
4. What is the state of Cobalt at room temperature?
5. Which period of the periodic table is Cobalt in?
Cobalt FAQs
What is the atomic number of cobalt?
Cobalt's atomic number is 27 — every cobalt atom has 27 protons in its nucleus.
What is the symbol for cobalt?
Co. From German Kobold, a goblin blamed for troublesome ores.
Is cobalt a metal, nonmetal, or metalloid?
Cobalt is classified as a transition metal.
What state is cobalt at room temperature?
At about 25 °C, cobalt is a solid. It melts at 1494.8 °C.
What is cobalt used for?
Key uses include: lithium-ion battery cathodes; superalloys for jet turbines; cobalt blue pigments in glass and ceramics.
Related elements
Keep working with this element
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