An iron atom has 26 electrons around its nucleus. There are 2 in the K shell, 8 in the L shell, 14 in the M shell and 2 in the N shell.
Iron can lose the two electrons in its outer N shell to become \mathrm{Fe}^{2+}, and it can also lose one more electron from the inner M shell to become \mathrm{Fe}^{3+}.
When iron is put into dilute sulfuric acid, it dissolves, giving off hydrogen, and forms a pale green solution containing \mathrm{Fe}^{2+}.
\mathrm{Fe} + \mathrm{H_2SO_4} \longrightarrow \mathrm{FeSO_4} + \mathrm{H_2}
\mathrm{Fe}^{2+} is easily oxidized by oxygen in the air, and it gradually changes into yellowish brown \mathrm{Fe}^{3+}.
When sodium hydroxide solution is added, \mathrm{Fe}^{2+} gives a greenish white precipitate of iron(II) hydroxide, and \mathrm{Fe}^{3+} gives a reddish brown precipitate of iron(III) hydroxide.
Iron that is in contact with both water and oxygen gradually rusts, forming red rust. The main component of red rust is hydrated iron(III) oxide. Iron in contact only with water that has been boiled to drive out the air, or only with dry air, hardly rusts at all.
The black rust that forms on the surface when iron is strongly heated, triiron tetraoxide, \mathrm{Fe_3O_4}, forms a film that protects the metal underneath.
To keep iron from rusting, it is coated with zinc to make galvanized iron, or with tin to make tinplate. Even if galvanized iron is scratched, the zinc, which forms ions more readily than iron, dissolves first, so the iron is still slow to rust.
The raw materials of iron are iron ores, such as haematite, \mathrm{Fe_2O_3}, and magnetite, \mathrm{Fe_3O_4}. Iron ore, coke and limestone are fed in at the top of a blast furnace, and hot air is blown in from below.
The carbon monoxide formed when the coke burns reduces the iron ore to iron.
\mathrm{Fe_2O_3} + 3\mathrm{CO} \longrightarrow 2\mathrm{Fe} + 3\mathrm{CO_2}
The molten iron collects at the bottom of the furnace and is tapped off as pig iron. The limestone combines with impurities in the iron ore to form slag, which floats on top of the pig iron and is removed.
Pig iron contains about 4 % carbon, and it is hard but brittle. When pig iron is moved to a converter and oxygen is blown in to reduce the carbon to 2 % or less, the result is called steel. Steel is tough, and it is used for the frames of buildings, rails, cars and much more.
An alloy of iron with chromium and nickel is called stainless steel, and because it resists rust, it is used for kitchen sinks and tableware.
In our blood, the iron in the haemoglobin of red blood cells carries oxygen.