30 Zn 65.38

Zinc

Transition metal Zincum solid

[Ar] 3d¹⁰ 4s² · 2 · 8 · 18 · 2

← Cu Copper Ga Gallium →

The metal that protects steel by destroying itself: a galvanised coating corrodes so the iron underneath does not. Zinc is also the second most important trace element for humans after iron.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 30
Atomic mass: 65.38 а.е.м.
Electron configuration: [Ar] 3d¹⁰ 4s²
Electrons per shell: 2 · 8 · 18 · 2
Block: d-block
Group: Zinc group
Period: 4
Electronegativity (Pauling): 1.65
Electronegativity (Allen): 1.59
Atomic radius: 142 pm
Covalent radius: 122 pm
Van der Waals radius: 139 pm
Ionisation energy 1: 906.4 kJ/mol
Ionisation energy 2: 1 733.3 kJ/mol
Ionisation energy 3: 3 833 kJ/mol
Ionisation energy 4: 5 731 kJ/mol
Ionisation energy 5: 7 970 kJ/mol
Electron affinity: 0 kJ/mol
Common oxidation states: +2
Oxidation states: -2, +1, +2

Physical properties

State at 25 °C: solid
Density: 7.14 g/cm³
Melting point: 692.68 K · 419.5 °C
Boiling point: 1 180 K · 906.9 °C
Speed of sound: 3 850 m/s

Thermal properties

Heat of fusion: 7.32 kJ/mol
Heat of vaporisation: 115 kJ/mol
Specific heat capacity: 0.388 J/(g·K)
Thermal conductivity: 116 W/(m·K)

Mechanical properties

Young's modulus: 108 GPa
Shear modulus: 43 GPa
Bulk modulus: 70 GPa
Poisson ratio: 0.25
Mohs hardness: 2.5
Brinell hardness: 412 MPa

Electrical and magnetic properties

Electrical resistivity: 59 nΩ·m
Magnetic ordering: diamagnetic
Curie point: no data
Néel point: no data
Superconducting point: 0.85 K

Crystal structure

Crystal structure: hexagonal close-packed (hcp)
Lattice constants: a = 266.49 pm · c = 494.68 pm

Abundance

In the crust: 70 mg/kg
In the ocean: 0.0049 mg/L
In the universe: 30 mg/kg
In the human body: 33 mg/kg

Isotopes

Isotope	Abundance	Half-life	Decay mode
⁶⁴Zn	49.17 %	stable	—
⁶⁶Zn	27.73 %	stable	—
⁶⁷Zn	4.04 %	stable	—
⁶⁸Zn	18.45 %	stable	—
⁷⁰Zn	0.61 %	stable	—

Five stable isotopes. Zinc-65 serves as a radiotracer in metabolic studies.

Discovery

Year of discovery: 1746
Discovered by: Andreas Sigismund Marggraf
Where: Germany
Origin of the name: from German Zinke (prong), the shape of zinc deposits in a furnace

History

Brass was smelted long before zinc was known as an element — the ore was simply added to copper. India was smelting zinc by the twelfth century; in Europe Marggraf recognised it as an element in 1746.

Where it occurs

70 mg/kg of the crust. The principal ore is sphalerite, ZnS, usually alongside lead. The largest producers are China, Peru and Australia.

How it is produced

Roasting sphalerite to the oxide, then either carbon reduction or sulfuric acid leaching and electrolysis. Electrolytic zinc reaches 99.995 %.

Role in living things

Zinc sits in over three hundred enzymes and in zinc fingers, the protein domains that read DNA sequences. Zinc deficiency stunts growth and weakens immunity, and is widespread in poorer countries.

Safety

Zinc compounds are of low toxicity, but inhaling zinc oxide fume while welding galvanised steel causes metal fume fever, a flu-like day of misery.

Uses

Galvanising steel — more than half of consumption
Brass and other alloys
Die-casting intricate components
Zinc oxide in rubber, sunscreens and ointments
Zinc-air and alkaline batteries

Curiosities

A galvanised surface shows a characteristic crystal pattern known as spangle.
Zinc protects steel even where the coating is scratched: the protection is electrochemical, not a barrier.
Zinc oxide is the one physical UV filter permitted in every jurisdiction.
Zinc fingers are the most common class of DNA-binding domain in the human genome.