Indium
Element 49 · Post-Transition Metal
Indium is a silvery, extremely soft metal that you have almost certainly touched today: a thin film of indium tin oxide (ITO) coats nearly every smartphone touchscreen and LCD display, conducting electricity while staying perfectly transparent. Indium melts at just 156.6 °C and wets glass and ceramics easily, which makes it useful in specialty solders and seals. Its compounds are also key semiconductors — indium phosphide is used in fiber-optic lasers and high-speed electronics. The element is named for the brilliant indigo line in its flame spectrum.
Key facts
| Atomic number | 49 |
|---|---|
| Atomic weight | 114.82 |
| Category | Post-Transition Metal |
| Group / Period | 13 / 5 |
| Block | p |
| Electron configuration | [Kr] 4d10 5s2 5p1 |
| Common oxidation states | +3, +1 |
| State at STP | Solid |
| Electronegativity | 1.78 |
| Atomic radius | 167 pm (empirical) |
| Density | 7.31 g/cm³ |
| Melting point | 156.6 °C |
| Boiling point | 2072 °C |
Occurrence
Indium occurs only in trace amounts, recovered as a by-product of zinc and tin refining. Its scarcity relative to demand from the electronics industry makes efficient recycling important.
Applications
Touchscreens (indium tin oxide)
Low-melting solders
Semiconductors (indium phosphide)
LCD displays
Common compounds
- Indium tin oxide
- Indium phosphide
- Indium nitride
Indium is so soft it can be scratched with a fingernail, and a bar of pure indium emits a high-pitched 'cry' when bent.
Data source: IUPAC standard atomic weights 2021; NIST physical property data