Indium (In)

Indium tin oxide is the material that made touchscreens possible: a coating that conducts electricity while being close to transparent, which almost nothing else does well. The metal is so soft it can be scratched with a fingernail and it screams faintly when bent, a crackling called the indium cry, caused by crystal twinning — tin does the same thing. It is produced entirely as a by-product of zinc refining, so world output is capped by how much zinc the world wants rather than by demand for indium.

Properties

Atomic number

49

Symbol

In

Standard atomic weight

114.82 u

Category

Post-transition metal

Group

13

Period

5

Block

p-block

Electron configuration

[Kr] 5s² 4d¹⁰ 5p¹

Electrons per shell

2, 8, 18, 18, 3

Melting point

429.75 K — 156.6 °C — 313.9 °F

Boiling point

2,345 K — 2071.8 °C — 3761.3 °F

Density

7.31 g/cm³

Electronegativity

1.78 (Pauling)

Oxidation states

+3

Discovered

1863 by Ferdinand Reich and Hieronymous Theodor Richter

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p¹

Noble gas shorthand

[Kr] 5s² 4d¹⁰ 5p¹

Shells

K: 2 · L: 8 · M: 18 · N: 18 · O: 3

What it is used for

• Indium tin oxide, the transparent conductor on every touchscreen and LCD
• Cold-weld seals and gaskets for ultra-high vacuum systems
• Low-melting alloys and thermal interface material
• Semiconductor compounds for infrared detectors and high-speed transistors
• Solder for joining glass, ceramics and cryogenic assemblies

Neighbours in the table

Group 13

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Indium sits in group 13 with boron, aluminum, gallium, thallium, nihonium.