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Indium

Indium (In) is a post-transition metal with atomic number 49 and an atomic mass of 114.82. Its electron configuration is [Kr] 4d10 5s2 5p1, which gives it 3 valence electrons.

Indium key data

Symbol In
Atomic number 49
Atomic mass (standard atomic weight) 114.82
Molar mass 114.82 g/mol
Protons 49
Neutrons (most abundant isotope, indium-115) 66
Electrons (neutral atom) 49
Valence electrons 3
Category Post-transition metal
Period 5
Group 13
Block p-block
Noble gas notation [Kr] 4d10 5s2 5p1
Full electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p1
Electrons per shell 2, 8, 18, 18, 3

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.

Measured properties of indium

From PubChem, the US National Institutes of Health. Public domain. The electron affinity is the measured value for indium, from Wikipedia’s electron affinity data page, in place of PubChem’s 0.3 eV.

Melting point 429.75 K (156.6 °C), 81st of 103 by melting point
Boiling point 2345 K (2071.9 °C), 51st of 93 by boiling point
Density 7.31 g/cm³, 43rd of 96 by density
State at room temperature Solid
Electronegativity 1.78 (Pauling), 43rd of 95 by electronegativity
Van der Waals radius 193 pm, 68th of 99 by atomic radius
First ionisation energy 5.786 eV (558.3 kJ/mol), 84th of 102 by first ionisation energy
Electron affinity 0.38392 eV (37.043 kJ/mol), 47th of 57 by electron affinity
Common oxidation states +3
Discovered 1863

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Indium electron configuration

The full electron configuration of indium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p1. With the noble-gas core collapsed it is [Kr] 4d10 5s2 5p1, and the outermost subshell is 5p1.

Bohr model of indium (In): a nucleus and five shells holding 2, 8, 18, 18 and 3 electrons from the inside out.
Bohr model of indium (In). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.
Orbital box diagram of indium (In), [Kr] 4d10 5s2 5p1, with the krypton core drawn as one bar: one box per orbital, filled by Hund’s rule, showing one unpaired electron, in 5p.
Orbital diagram of indium (In). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one indium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

  1. one atom = 114.82 / (6.02214076 × 10²³)
  2. = 1.9066 × 10⁻²² g

Atoms in one gram

  1. atoms per gram = 6.02214076 × 10²³ / 114.82
  2. = 5.2449 × 10²¹ atoms

Indium on the periodic table

Indium is in period 5, group 13, in the p-block.

The other elements of group 13 are boron, aluminium, gallium, thallium and nihonium.

The rest of period 5

Work with indium