Cobalt

Transition metal · atomic number 27

2758.9331944CoCobaltSolidTransition metal

Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's crust is found only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.

Properties of Cobalt

Element category	Transition metal
Atomic number	27
Atomic mass	58.9331944 u
Phase at STP	Solid
Group	9
Period	4
Block	d
Electron configuration	[Ar] 3d7 4s2
Electrons per shell	2, 8, 15, 2
Electronegativity (Pauling)	1.88
Melting point	1768 K (1495 °C)
Boiling point	3200 K (2927 °C)
Density	8.9 g/cm3
Discovered by	Georg Brandt

← Iron · Periodic table · Nickel → Ni

About the transition metal group

The dense, strong, catalytic heart of the table — iron, copper, gold, titanium — responsible for most of metallurgy, jewellery and industry.

Data: Periodic-Table-JSON (CC BY-SA 3.0) · stored statically on our server. https://en.wikipedia.org/wiki/Cobalt

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🧪 Reactive nonmetal

11 elements: Elements that readily gain or share electrons — the building blocks of water, air, living tissue and most organic chemistry.

🧪 Noble gas

6 elements: Full outer electron shells make these gases almost inert: they barely react, glow in discharge lamps and are used to create unreactive atmospheres.

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6 elements: Soft, wildly reactive metals of group 1 — they fizz in water and never occur pure in nature. Lithium, sodium, potassium and friends.

🧪 Alkaline earth metal

6 elements: Reactive group-2 metals a step calmer than the alkalis: magnesium, calcium and the structural and biological workhorses among them.

🧪 Transition metal

35 elements: The dense, strong, catalytic heart of the table — iron, copper, gold, titanium — responsible for most of metallurgy, jewellery and industry.

🧪 Post-transition metal

9 elements: Softer, lower-melting metals beside the transition block — aluminium, tin, lead — abundant in cans, foils, solders and pigments.

🧪 Metalloid

7 elements: In-between elements that behave as semiconductors: silicon, germanium and boron underpin electronics, glass and solar cells.

🧪 Lanthanide

15 elements: The rare-earth “inner transition” metals that give strong permanent magnets, screen phosphors and catalyst polish.

🧪 Actinide

15 elements: Mostly radioactive, heavy metals — several made only in reactors — whose fission powers nuclear energy and weapons.

🧪 Unknown properties

8 elements: Superheavy synthetic elements made atom-by-atom, existing for fractions of a second; their true chemistry is still unmeasured.