All practice pages/Interatomic theory/Elements
Element 49, a post-transition metal
A metal soft enough to scratch with a fingernail, and the transparent conductor on every touchscreen.
Period 5, group 13. The other post-transition metals are tinted, and every cell opens its own article.
Indium has 49 electrons, one for every proton, so the atom carries no charge. Below are the same 49 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p¹
Short form: [Kr] 4d¹⁰ 5s² 5p¹, where [Kr] stands for the 36 electrons krypton already has.
That list runs by shell. In the order the subshells fill it reads [Kr] 5s² 4d¹⁰ 5p¹, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 3 here is 3s² 3p⁶ 3d¹⁰, and 2 + 6 + 10 is 18.
Indium sits in period 5 and has 5 shells. The period number counts the shells.
The outer shell holds 3 electrons. Those are the ones indium can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 13 means 3.
A metal that gives up its valence electrons to form positive ions, though less readily than the metals to its left.
Rare and never mined for itself. It is recovered from zinc ores during refining, mostly in China and South Korea.
Ferdinand Reich and Hieronymus Theodor Richter found it in 1863 while examining zinc ore with a spectroscope. Reich was color-blind, so Richter was the one who saw the bright indigo line that gave the element its name.
Most becomes indium tin oxide, a transparent film that conducts electricity on touchscreens, flat-panel displays and some solar cells. Indium also goes into low-melting solders, semiconductors such as the indium gallium nitride in LEDs, and seals for very cold equipment.