How the character is built
The 石 radical marks this as a solid non-metal, and that is not a coincidence of this one character — it holds right across the table. Read the radical first and the element's state at room temperature is already settled.
Where you actually meet it
碘盐 (diǎnyán) iodised salt
The element itself
Solid iodine sublimes straight to a violet vapour when warmed, skipping the liquid entirely, and it was named for that colour. Unusually for a mined commodity it comes largely from two odd sources: the same Chilean nitrate caliche that supplied the world's fertiliser before industrial fixation, and the deep brines that come up with natural gas beneath Chiba in Japan — ancient seawater that concentrated iodine from the marine life that settled into it.
Where it sits among the 118
First isolated in 1811.
In living things
Thyroid hormone is essentially a molecule for carrying iodine: thyroxine is two linked tyrosine rings decorated with four iodine atoms, which is why it is called T4, and enzymes activate it by plucking exactly one atom off to give T3. To assemble it the thyroid runs a dedicated pump, the sodium–iodide symporter, which concentrates iodide from the blood many times over — a gland built around scavenging a scarce element. Iodine is scarce because it is volatile and marine: it cycles out of the sea into the air and rains down near coasts, leaving mountain interiors and long-leached soils with very little of it, which is a geography story as much as a biological one.
The full entry
For stroke order, example sentences, audio and the complete set of meanings, see the dictionary entry.
碘Iodine in the dictionary →Others built the same way
Every one of these carries 石, and every one is a solid non-metal.