What Is Indium?
Indium is a chemical element with the symbol In and atomic number 49, categorized as a post-transition metal.
A soft, silvery-white metal. Used in touchscreen displays as transparent ITO coating.
As a post-transition metal in Period 5 and Group 13 (Boron Group), indium's placement on the table reflects its electron configuration of [Kr] 4d¹⁰ 5s² 5p¹, which governs its bonding behavior and the type of compounds it typically forms.
Position on the Periodic Table
Indium is located in Period 5, which continues the transition metal pattern seen in Period 4 but one principal shell further out.
Within that row, indium sits in Group 13 (Boron Group), alongside elements that share a similar number of valence electrons and, by extension, similar chemical behavior.
This position is not arbitrary — the periodic table was deliberately organized so that an element's row and column reveal its expected reactivity, bonding pattern, and physical state at a glance.
Physical & Chemical Properties
Indium has an atomic mass of 114.818 u and a density of 7.31 g/cm³. Its melting point is 156.6°C and its boiling point is 2072°C.
Indium is generally softer and lower-melting than the transition metals positioned to its left on the periodic table.
Electron Configuration Explained
Indium's electron configuration is [Kr] 4d¹⁰ 5s² 5p¹, describing how its electrons are distributed across shells and subshells around the nucleus.
Reading the configuration in order shows electrons filling shells of increasing energy, following the standard Aufbau principle that explains how atomic structure builds up across the periodic table.
The outermost (valence) electrons shown in this configuration are what ultimately determine indium's chemical reactivity and the type of bonds it forms with other elements.
History & Discovery
Indium was formally discovered in 1863, Reich & Richter, identified through the careful isolation and analytical techniques typical of that era's chemical research.
Many elements from this period were anticipated by Dmitri Mendeleev's periodic table, which successfully predicted gaps corresponding to undiscovered elements well before laboratory instruments existed to confirm them directly.
What Is Indium Used For?
Indium's specific properties make it useful in several applications, including:
- Touchscreen coatings (ITO)
- Solders
- Semiconductors
- Bearings
- Low-melting alloys
These uses reflect indium's underlying classification as a post-transition metal, since the same properties that define its category in chemistry also determine where it becomes practically useful.
Fun Facts About Indium
- Every smartphone touchscreen contains indium — used as transparent conductor ITO.
- Indium is element number 49 on the periodic table, in Period 5 and Group 13.
- Its standard atomic mass is 114.818 u, calculated from the natural abundance of its isotopes.
Frequently Asked Questions
What is Indium's atomic number?
Indium has atomic number 49.
What is Indium's chemical symbol?
Indium's symbol is In.
What group and period is Indium in?
Indium is in Period 5, Group 13 (Boron Group).
What is Indium's atomic mass?
Indium's standard atomic mass is 114.818 u.