Indium (In)
Post-transition metal
Indium is a soft, silvery metal you have probably touched today — indirectly. Indium tin oxide is the transparent conductor coating virtually every phone and laptop touchscreen.
Position on the periodic table
Atomic properties
| Atomic number | 49 |
|---|---|
| Atomic mass | 114.818 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p1 |
| Noble gas shorthand | [Kr] 4d10 5s2 5p1 |
| Electrons per shell | 2, 8, 18, 18, 3 |
| Valence electrons (outer shell) | 3 |
| Common oxidation states | +3 |
| Electronegativity (Pauling) | 1.78 |
| Covalent radius (approx.) | 142 pm |
| First ionization energy | 558.3 kJ/mol |
| Electron affinity | 37 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 7.31 g/cm³ |
| Melting point | 156.6 °C (429.75 K) |
| Boiling point | 2071.8 °C (2345 K) |
| Appearance | silvery lustrous gray |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of indium
Indium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p1, usually shortened to [Kr] 4d10 5s2 5p1. Its electrons occupy 5 shells (2, 8, 18, 18, 3), placing it in period 5 of the p-block. The 3 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of indium
- Touchscreens and flat displays (indium tin oxide)
- Low-melting solders and seals
- Semiconductors and LEDs (InP, InGaN)
- Cryogenic gaskets
Biological role: None known.
Occurrence: A rare by-product of zinc smelting.
Common compounds of indium
In2O3
Indium(III) oxide
InP
Indium phosphide
History and discovery
Discovered: 1863 — Ferdinand Reich. Name origin: From the indigo-blue line in its atomic spectrum.
Ferdinand Reich and Hieronymous Richter found indium in 1863 while searching zinc ore spectra for thallium.
Safety notes
Bulk metal is low-risk; inhaled indium compounds in industry require strict controls.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Indium
1. What is the chemical symbol of Indium?
2. What is the atomic number of Indium?
3. Which category does Indium belong to?
4. What is the state of Indium at room temperature?
5. Which period of the periodic table is Indium in?
Indium FAQs
What is the atomic number of indium?
Indium's atomic number is 49 — every indium atom has 49 protons in its nucleus.
What is the symbol for indium?
In. From the indigo-blue line in its atomic spectrum.
Is indium a metal, nonmetal, or metalloid?
Indium is classified as a post-transition metal.
What state is indium at room temperature?
At about 25 °C, indium is a solid. It melts at 156.6 °C.
How many valence electrons does indium have?
Indium has 3 electrons in its outer shell (shell pattern: 2, 8, 18, 18, 3).
What is indium used for?
Key uses include: touchscreens and flat displays (indium tin oxide); low-melting solders and seals; semiconductors and leds (inp, ingan).
Related elements
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