Indium
[Kr] 4d¹⁰ 5s² 5p¹ · 2 · 8 · 18 · 18 · 3
The softest of metals — soft enough to leave a mark on paper — and the key ingredient of the transparent conductor without which no touchscreen works.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 49
- Atomic mass
- 114.818 а.е.м.
- Electron configuration
- [Kr] 4d¹⁰ 5s² 5p¹
- Electrons per shell
- 2 · 8 · 18 · 18 · 3
- Block
- p-block
- Group
- Boron group
- Period
- 5
- Electronegativity (Pauling)
- 1.78
- Electronegativity (Allen)
- 1.66
- Atomic radius
- 156 pm
- Covalent radius
- 142 pm
- Van der Waals radius
- 193 pm
- Ionisation energy 1
- 558.3 kJ/mol
- Ionisation energy 2
- 1 820.7 kJ/mol
- Ionisation energy 3
- 2 704 kJ/mol
- Ionisation energy 4
- 5 210 kJ/mol
- Electron affinity
- 28.9 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- -5, -2, -1, +1, +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 7.31 g/cm³
- Melting point
- 429.75 K · 156.6 °C
- Boiling point
- 2 345 K · 2 071.9 °C
- Speed of sound
- 1 215 m/s
Thermal properties
- Heat of fusion
- 3.281 kJ/mol
- Heat of vaporisation
- 231.8 kJ/mol
- Specific heat capacity
- 0.233 J/(g·K)
- Thermal conductivity
- 81.8 W/(m·K)
Mechanical properties
- Young's modulus
- 11 GPa
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- 0.45
- Mohs hardness
- 1.2
- Brinell hardness
- 8.8 MPa
Electrical and magnetic properties
- Electrical resistivity
- 83.7 nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 3.41 K
Crystal structure
- Crystal structure
- tetragonal
- Lattice constants
- a = 325.23 pm · c = 494.61 pm
Abundance
- In the crust
- 0.25 mg/kg
- In the ocean
- 1·10⁻⁷ mg/L
- In the universe
- 0.003 mg/kg
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 113In | 4.29 % | stable | — |
| 115In | 95.71 % | 440 473.47 Gyr | β− |
Indium-115 is 96 % of natural indium and faintly radioactive, with a half-life of 4.4·10¹⁴ years — thirty thousand times the age of the universe.
Discovery
- Year of discovery
- 1863
- Discovered by
- Ferdinand Reich and Hieronymous Richter
- Where
- Germany
- Origin of the name
- after the indigo line in its spectrum
History
Reich and Richter were hunting thallium in zinc blende with a spectroscope in 1863 when they saw an unfamiliar bright indigo line. It named the element.
Where it occurs
0.25 mg/kg of the crust. It has no ores of its own and is dispersed through zinc and tin concentrates.
How it is produced
From zinc production residues by electrolytic deposition. World output is under a thousand tonnes a year, and supply depends entirely on the zinc industry.
Role in living things
No biological role.
Safety
Inhaled indium compounds cause pulmonary fibrosis; the condition was described in workers making ITO sputtering targets and is known as indium lung.
Uses
- Indium tin oxide (ITO): the transparent electrode of LCD and OLED screens and touch panels
- Low-melting solders for joining fragile materials
- Seals for cryogenic vacuum systems: indium stays ductile even at 4 K
- Semiconductors: indium arsenide and phosphide in high-frequency devices
Curiosities
- Indium's principal isotope is radioactive, so all natural indium is formally unstable.
- Indium gives a characteristic cry when bent, as tin does.
- Every touchscreen in the world holds a thin layer of indium tin oxide.
- Indium is soft enough to write with, like a pencil.