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Indium (In)
Indium (symbol In) is the chemical element with atomic number 49: a post-transition metal, solid at 0 °C, with an atomic mass of 114.82 u. Discovered in 1863 (Ferdinand Reich and Theodor Richter).
Indium is a metal so soft you can scratch it with a fingernail. Combined with tin oxide, it forms ITO, a material that is both transparent and electrically conductive, essential for flat screens and touchscreens. Rare and produced in small quantities, it is considered critical by many countries.
Key facts
- Atomic number
- 49
- Symbol
- In
- French name
- Indium
- Atomic mass
- 114.82 u
- Molar mass
- 114.82 g/mol
- Family
- Post-transition metals
- Position
- period 5, group 13, p-block
- State at 0 °C
- Solid
- Melting point
- 156.6 °C
- Boiling point
- 2,071.9 °C
- Density
- 7.31 g/cm³
- Electronegativity (Pauling)
- 1.78
- First ionization energy
- 558 kJ/mol
- Atomic radius
- 155 pm
- Electron configuration
- [Kr] 4d¹⁰ 5s² 5p¹
- Abundance in Earth's crust
- 0.25 ppm (64th most abundant element)
- Indicative price
- 170 $/kg (order of magnitude)
- Radioactive
- no
- Discovery
- 1863, Ferdinand Reich and Theodor Richter
Origin of the name
From the indigo line in its spectrum.
What does indium look like?
A shiny, silvery-white metal, softer than lead. Like tin, it gives a faint “cry” when bent, caused by its crystals rubbing together.
Where is indium found?
About 0.05 ppm of Earth's crust, making it about as rare as silver. It is present as traces in zinc ores.
Natural sources
- Sphalerite (traces)
- Roquesite (rare)
How is indium produced?
It is recovered from zinc refining residues. World refined output is about 1,000 tonnes a year, more than half of it in China, supplemented by extensive recycling of screen-manufacturing scrap.
Top producers
- China
- South Korea
- Japan
- Canada
What is indium used for?
- Indium tin oxide (ITO) layers in flat screens and touchscreens.
- Low-melting-point solders.
- Semiconductors (LEDs, fiber-optic lasers).
- Thin-film solar cells (CIGS).
- Airtight seals for cryogenics.
In everyday life
- Smartphone touchscreen
- Flat-screen TV
- De-icing cockpit windshield
Role in living things
No known biological role.
Hazards of indium
Low toxicity when swallowed, but inhaling ITO dust has given workers a serious lung disease, “indium lung.”
Cosmic origin
- Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
- Neutron stars: Created when two neutron stars collide — the “forge” of gold.
History of indium
In 1863, in Freiberg, Ferdinand Reich and Hieronymus Theodor Richter were looking for thallium in a zinc ore. Since Reich was color-blind, it was Richter who saw an unknown indigo-blue line in the spectroscope, which gave the element its name. Richter later claimed sole credit for the discovery, to Reich's fury.
Did you know?
- Indium wets glass: when molten, it sticks to it and is used to make perfectly airtight seals.
- A smartphone screen contains only a few milligrams of indium, in a layer thinner than a soap bubble.
- Alloyed with gallium and tin, it forms Galinstan, which is liquid at room temperature.
Isotopes of indium
A single stable isotope, indium-113, and a small minority at that: 96% of natural indium is indium-115, radioactive but with a half-life 30,000 times the age of the Universe.
- indium-111: radioactive, half-life 2.8 days. Labels white blood cells to locate an infection by scintigraphy.
- indium-113: 4.29% of natural indium, stable
- indium-113m: radioactive, half-life 1.66 h
- indium-115: 95.71% of natural indium, radioactive, half-life 4.41 × 10¹⁴ years
Related elements
Same family (post-transition metals): Aluminium (Al), Gallium (Ga), Tin (Sn), Thallium (Tl), Lead (Pb), Bismuth (Bi), Polonium (Po).
Same column (group 13): Boron (B), Aluminium (Al), Gallium (Ga), Thallium (Tl), Nihonium (Nh).