Write the formula for indium(III) phosphide, a semiconductor laser material.
In3+ with P3- pairs one-to-one: InP. Fiber-optic network lasers are built on this crystal and its relatives.
What Is the Charge of Indium?
Indium commonly forms In+ In3+ in introductory ionic compounds.
Indium's standard charge is +3 — In2O3 is the basis of the transparent ITO electrodes in nearly every touchscreen. A genuine +1 state (InCl exists as a solid) marks the onset of the inert-pair effect, but +3 answers any ordinary problem.
| Element | Indium |
|---|---|
| Symbol | In |
| Atomic number | 49 |
| Common ionic charge | +1, +3 |
| Common ions | In+, In3+ |
Visual reference
Indium element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
How Indium's outer electrons decide its charge
Indium is [Kr]4d10 5s2 5p1. Giving up all three outer electrons yields In3+. Down this group the 5s pair grows reluctant to participate — the relativistic 'inert pair' — so +1 compounds start appearing at indium and take over completely at thallium below it.
The Indium mistake worth a warning
Balancing indium(III) compounds with +1 arithmetic. Indium tin oxide's workhorse component is In2O3: two In3+ (+6) with three O2- (-6). If a formula problem says indium without a numeral, +3 is the safe assumption.
Worked example: In in a formula problem
In+ and In3+ in real compounds
InCl
Indium chloride
In+ balances chloride ions.
In2O
Indium oxide
Indium can form oxides where total positive and negative charge balances.
Questions students ask about indium
What makes ITO both transparent and conductive?
In2O3 is a wide-gap oxide (transparent) whose tin doping donates mobile electrons (conductive). Indium sits at +3 throughout; the borrowed electrons do the conducting. Every phone screen taps through it.
Why does indium 'cry' when bent?
The squeal is crystal twinning in the neutral metal — a mechanical quirk shared with tin. No ions involved; indium's softness also lets it seal cryogenic equipment like a metallic gasket.
Is indium scarce?
It is mined only as a zinc byproduct (a fellow traveler of Zn2+ in ores), and touchscreen demand has made recycling ITO sputtering waste a real industry.
How do I use this charge in formulas?
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
Where this data comes from
Charges and element facts on this page are checked against the primary references below. Found an error? Email hello@periodictablewithcharges.com — corrections ship in the next content update. See how this site is edited.