All practice pages/Interatomic theory/Elements
Element 26, a transition metal
The metal of civilization since the Iron Age, the heart of our planet, and the atom that carries oxygen in your blood.
Period 4, group 8. The other transition metals are tinted, and every cell opens its own article.
Iron has 26 electrons, one for every proton, so the atom carries no charge. Below are the same 26 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²
Short form: [Ar] 3d⁶ 4s², where [Ar] stands for the 18 electrons argon already has.
That list runs by shell. In the order the subshells fill it reads [Ar] 4s² 3d⁶, 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 3d⁶, and 2 + 6 + 6 is 14.
Iron sits in period 4 and has 4 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones iron can lose, gain or share, so they are the ones that decide what it bonds with.
Iron gives up two electrons to form Fe²⁺ or three to form Fe³⁺. Having two common ions is why its compounds are named with Roman numerals, as in iron(III) oxide.
By mass, the most abundant element in the Earth as a whole, because the core is mostly iron and nickel, and the fourth most abundant in the crust, about 5%. It is mined as hematite (Fe₂O₃) and magnetite (Fe₃O₄), above all in Australia and Brazil. Some meteorites are almost pure iron-nickel metal.
Known since ancient times. The earliest iron objects were hammered from meteorites, and smelting iron from ore became widespread around 1200 BCE, beginning the Iron Age. The name is Old English; the symbol Fe comes from its Latin name, ferrum.
Steel, which is iron with a little carbon, is by far the most used metal: buildings, bridges, cars, ships, pipes, cans and tools. Cast iron makes pans and engine blocks. Iron oxides color paint, bricks and pottery, and iron is an essential nutrient, since hemoglobin in red blood cells uses it to carry oxygen.