Chemical element · reference page

49In

Indium

Indium is element 49 (In), located in period 5, group 13 and the p block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 4d10 5s2 5p1.

Atomic number49

Standard atomic weight114.818(1)

Group13

Period5

Blockp

Electron configuration[Kr] 4d10 5s2 5p1

Electronic structure

What controls its chemistry

Atoms in group 13 have three valence electrons in the outer s and p subshells. The balance between covalent bonding and positive oxidation states changes down the group as atomic size and metallic character increase.

Indium is therefore best understood by comparing it with the elements immediately above and below it rather than by treating group 13 as chemically uniform.

Chemical forms

Compounds, ions and materials

Group 13 chemistry includes oxides, halides and covalent or ionic compounds in positive oxidation states. The lighter elements show more covalent character, while the heavier members become progressively more metallic.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 7.31 g/cm³. The melting point is 429.7 K (156.6 °C). The boiling point is 2 345 K (2 072 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where indium is found and used

In practice, indium is encountered in touch screens, semiconductors and alloys.

In practice

Examples of real uses

Touch screens

Transparent conducting layers use indium compounds to combine electrical conduction with optical transparency.

Semiconductors

Compounds or doped forms of indium are used to control electrical conduction in semiconductor devices.

Alloys

Indium is added to metals to change strength, corrosion resistance, melting behaviour or high-temperature performance.

Periodic position

What its neighbours tell us

Indium is in period 5 and group 13. In the neighbourhood shown here, it lies between cadmium and tin in the same period; gallium is above it and thallium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationpost-transition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 18 · 3

Density7.31 g/cm³

Melting point429.7 K (156.6 °C)

Boiling point2 345 K (2 072 °C)

Pauling electronegativity1.78

First ionisation energy558.3 kJ/mol

Electron affinity37.04 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of indium is associated with Ferdinand Reich. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 114.818(1). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Indium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with indium depend on chemical form, dose and route of exposure. Pure indium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.