Indium (In)
“Soft enough to scratch with a fingernail — yet a film of its oxide hides beneath every smartphone touchscreen on Earth.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Kr] 4d¹⁰ 5s² 5p¹: a soft post-transition metal of Group 13, Period 5, p-block, with three valence electrons; it usually forms In³⁺ in compounds such as In₂O₃.
- Among the softest of all metals (Mohs hardness about 1.2) — it takes a fingernail scratch and melts on a hot pan at 156.6 °C, both signs of weak metallic bonding.
- It clings to and “wets” glass, and its oxide alloy with tin forms ITO — a film that conducts electricity yet stays almost perfectly transparent.
- Bending a strip produces the same crackling “cry” as tin, caused by crystal twins snapping inside the metal lattice.
An extremely soft, silvery-white metal that slices like cheese and takes a mark from a fingernail. It melts at only 156.6 °C, and bending a thin strip gives a soft crackling “cry” as its crystals deform.
Where you meet it
✦ Uses
- Indium tin oxide (ITO) — the invisible conducting layer on smartphone, tablet and ATM touchscreens that senses exactly where a finger lands.
- Indium gallium nitride (InGaN) layers that emit the blue and green light of LED bulbs and screens — the heart of the 2014 Nobel-Prize blue LED.
- Low-melting solders and fusible alloys (indium-tin, indium-bismuth) that flow below 150 °C for joining heat-sensitive electronics.
- InGaAs infrared detectors for night-vision cameras, TV remotes and fibre-optic communication receivers.
◍ Everyday examples
- The screen you tap on any smartphone, tablet or laptop hides a film of indium tin oxide just nanometres thick.
- A white LED bulb and the TV remote’s invisible flash both run on indium-based compound semiconductors.
- Indium almost never forms its own ore; virtually all of it is recovered as a byproduct of zinc smelting.
History & name
In 1863 the German physicists Ferdinand Reich and Hieronymous Theodor Richter were examining sphalerite (zinc-blende) ores with a spectroscope at Freiberg when a brilliant indigo-blue line appeared that matched no known element. Reich was colour-blind, so it was Richter who judged the line’s hue — and the pair named the new metal indium after indigo. Richter isolated the metal soon after, making indium one of the first elements discovered purely from the colours of its glowing vapour.