ChemSphere
49In114.818

Indium

Post-transition metal · Period 5 · Group 13 · p-block

The soft metal that makes touchscreens possible

Atomic mass
114.818 u
State at 25 °C
Solid
Electronegativity
1.78
Melting point
156.6 °C
Boiling point
2,071.9 °C
Configuration
[Kr] 4d10 5s2 5p1
Building atom…
49 protons 66 neutrons 49 electrons

Nucleus drawn at reduced count for clarity. Drag to rotate.

Indium, explained

Video lesson in production

Bhavya’s explainer for this element will play here.

Overview

Indium is a very soft, silvery metal in group 13, below gallium and above thallium. Its configuration is [Kr] 4d10 5s2 5p1, and it usually loses all three outer electrons to form In^3+, though the +1 state also exists. Indium melts at just 157 °C and is soft enough to scratch with a fingernail. A bar bent near the ear makes a faint crackling 'cry' as crystal twins form inside it, and the clean metal wets glass, sticking to it so well that it is used to make vacuum seals at cryogenic temperatures.

Most indium goes into indium tin oxide (ITO), a ceramic that is both transparent to visible light and electrically conducting. Those two properties rarely coexist: ITO's tin atoms donate free electrons, while its wide band gap lets visible light pass. Thin ITO films form the invisible electrodes in nearly every touchscreen, LCD and OLED panel. Indium also forms important semiconductors. Indium gallium nitride produces the blue light of white LEDs, and indium phosphide lasers drive fibre-optic links. Because indium is recovered only as a by-product of zinc refining, supply cannot easily expand with demand.

Discovery

In 1863 Ferdinand Reich and Hieronymous Theodor Richter at the Freiberg Mining Academy in Saxony were searching zinc ores for thallium. Because Reich was colour-blind, Richter examined the samples in a spectroscope and saw a brilliant indigo-blue line that matched no known element. They named it indium after the colour, from the Latin indicum, meaning indigo. Richter isolated the metal in 1864, and a sample was shown at the 1867 Paris Exposition.

Where it’s found
Indium makes up about 0.05 parts per million of the crust and is recovered mostly from residues of zinc refining, especially from sphalerite ores.
What it’s used for
  • Touchscreen electrodes (ITO)
  • Flat-panel displays
  • Blue and white LEDs
  • Low-melting solders
  • Cryogenic seals
  • Fibre-optic lasers
In living things
Indium has no known biological role. Its compounds have moderate toxicity, and inhaling indium tin oxide dust in factories has been linked to serious lung disease.
Safety
Bulk indium is safe to handle, but indium compound dusts should not be inhaled, and indium-111 used in medicine is radioactive.

How it compares

Where Indium sits among all 118 elements on the trends that shape the table.

  • Electronegativity1.78Pauling

    #44 of 100 elements with data

  • Ionization energy558kJ/mol

    #85 of 104 elements with data

  • Atomic radius155pm

    #40 of 95 elements with data

  • Electron affinity37kJ/mol

    #61 of 109 elements with data

  • Density7.31g/cm³

    #59 of 114 elements with data

  • Melting point430K

    #86 of 110 elements with data

Density
7.31 g/cm³
Atomic radius
155 pm
Covalent radius
142 pm
Molar heat
26.74 J/(mol·K)
Appearance
silvery lustrous gray
Discovered by
Ferdinand Reich

Inside the atom

49 electrons arranged in 5 shells: 2 · 8 · 18 · 18 · 3.

Orbital diagram

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p1 · shorthand [Kr] 4d10 5s2 5p1

  1. 1s2
  2. 2s2
  3. 2p6
  4. 3s2
  5. 3p6
  6. 4s2
  7. 3d10
  8. 4p6
  9. 5s2
  10. 4d10
  11. 5p1

Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Indium bonds.

Ionization energies

Energy to remove each electron in turn, on a log scale. The biggest leap, from electron 1 to 2 (×3.3), is where the next electron has to come from a filled shell much closer to the nucleus.

Signature reactions

The chemistry Indium is known for.

  1. Redox · Combustion

    Burning in air

    Indium burns with a violet-blue flame to form yellow indium(III) oxide. Mixed with a little tin oxide, the same compound becomes the transparent conductor ITO.

    4In(s)+3O2(g)2In2O3(s)

    Conditions: strong heating

  2. Redox · Single displacement

    Dissolving in hydrochloric acid

    Indium sits above hydrogen in the activity series, so it slowly dissolves in acids and releases hydrogen. The resulting indium chloride solution is used to recover and purify the metal.

    2In(s)+6HCl(aq)2InCl3(aq)+3H2(g)

    Conditions: warm dilute acid

  3. Thermal decomposition · Thin-film growth

    Growing indium phosphide

    Vapours of trimethylindium and phosphine react on a hot wafer, laying down a crystalline indium phosphide film one atomic layer at a time. These films become the lasers and detectors of fibre-optic networks.

    In(CH3)3(g)+PH3(g)InP(s)+3CH4(g)

    Conditions: metal-organic vapour-phase epitaxy, 500–650 °C

Where you’ll meet it

  • Touchscreen

    Touchscreen

    Transparent indium tin oxide electrodes detect the position of your finger on most touchscreens.

    Photo: Wikimedia Commons
  • Indium tin oxide

    Indium tin oxide

    Transparent indium tin oxide films conduct electricity, and are used to heat aircraft cockpit windows as well as in display screens.

    Photo: Wikimedia Commons
  • Light-emitting diode

    Light-emitting diode

    Blue and white LEDs emit light from layers of indium gallium nitride.

    Photo: Wikimedia Commons
  • Sphalerite

    Sphalerite

    Indium is extracted as a by-product from zinc ores such as sphalerite.

    Photo: Wikimedia Commons

Research

No research on Indium yet

When Bhavya publishes a project that studies Indium, it will be linked here.

See all research