Indium (In)
Element 49 · Post-transition metal · atomic mass 114.82 u · group 13, period 5
Electron shells: 2, 8, 18, 18, 3
Indium is soft enough to mark paper and sticks tenaciously to glass. Indium tin oxide is the transparent conductor behind virtually every touchscreen.
Every touchscreen you use works because indium tin oxide is both transparent and conductive.
- Atomic number
- 49
- Atomic mass
- 114.82 u
- Electron configuration
- [Kr] 5s² 4d¹⁰ 5p¹
- Group · period · block
- 13 · 5 · p
- Oxidation states
- +3
- Electronegativity
- 1.78 (Pauling)
- Melting point
- 157 °C
- Boiling point
- 2,072 °C
- Density
- 7.31 g/cm³
- State at 20 °C
- Solid
- Appearance
- Soft, silvery-white metal
- Discovered
- Ferdinand Reich and Hieronymous Theodor Richter, 1863
49 protons, and 49 electrons when neutral
IUPAC standard atomic weight
Boron group
What Indium is used for
- Indium tin oxide touchscreens and displays
- Low-melting solders and seals
- Semiconductors and photodetectors
- Cryogenic gaskets
Atomic structure of Indium
A neutral indium atom has 49 protons and 49 electrons. Its most common isotope carries about 66 neutrons, which is where the mass number 115 comes from. Change the neutron count and you have a different isotope of indium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 18, 3. In orbital notation that is [Kr] 5s² 4d¹⁰ 5p¹, leaving 3 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Indium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Indium sits in the periodic table
Metals to the right of the d-block. Softer, lower-melting and more brittle than the transition metals, with more covalent character in their bonding.
Discovery and naming
Indium was discovered by Ferdinand Reich and Hieronymous Theodor Richter in 1863. Its name comes from The indigo line in its spectrum.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Indium?
The standard atomic weight of Indium is 114.82 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Indium have?
Indium has 49 protons, because the atomic number is the proton count and that is what makes an atom Indium at all. A neutral Indium atom has the same number of electrons, 49. The neutron count varies by isotope; the most common one has about 66, since 115 − 49 = 66.
What is the electron configuration of Indium?
The electron configuration of Indium is [Kr] 5s² 4d¹⁰ 5p¹. Its electrons are arranged 2, 8, 18, 18, 3 across 5 shells.
Is Indium a metal?
Yes. Indium is classified as a post-transition metal, on the metallic side of the table.
What group and period is Indium in?
Indium is in group 13 (the boron group), period 5, in the p-block. The group is its column and the period is its row.
What is the charge of Indium?
Indium most commonly forms a 3+ ion. It has 3 outer electrons available to lose.
What is the melting point of Indium?
Indium melts at 157 °C and boils at 2,072 °C. That puts it in the solids at everyday temperatures.
What is Indium used for?
Indium tin oxide touchscreens and displays, Low-melting solders and seals, Semiconductors and photodetectors, Cryogenic gaskets. Indium is soft enough to mark paper and sticks tenaciously to glass.
Who discovered Indium, and where does its name come from?
Indium (In) was discovered by Ferdinand Reich and Hieronymous Theodor Richter in 1863. The name comes from The indigo line in its spectrum.