How the character is built
The 钅 radical marks this as a 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. It is 金 (jīn) squeezed into the space beside another component — radicals change shape by position, which is why 金 is hard to spot until you know to look for 钅.
Phonetic 它 tā 'it'; read tuó the same character is the sliding weight of a steelyard balance.
This character is used for the element and little else — you are unlikely to meet it outside a chemistry classroom.
The element itself
Thallium was found by its spectrum — a single vivid green line, which gave it a name from the Greek for a green shoot — during the same burst of spectroscopic discovery that turned up caesium and rubidium. It is a soft, dull metal that has no ore worth mining and is collected instead from the dusts and residues of roasting pyrite and smelting lead and zinc. Chemically it is a wolf in sheep's clothing: the thallium ion is close enough to potassium in size that biological systems handle it as though it were potassium, which is precisely why it is so dangerous.
Where it sits among the 118
First isolated in 1861.
In living things
Thallium is dangerous because of a coincidence of size. The Tl⁺ ion carries a single positive charge and is close enough to potassium in size — a shade larger — that potassium channels and the sodium–potassium pump wave it through without noticing; the pump in fact grips it more tightly than the potassium it is built to carry, so thallium distributes itself into every cell in the body rather than concentrating anywhere convenient. Colourless, tasteless and slow-acting, it earned a grim reputation in the era before analytical chemistry could look for it. The same mimicry has a legitimate use: a radioactive isotope of thallium follows potassium into well-perfused heart muscle, which makes it a tracer for imaging blood supply.
Where it comes from in China
Thallium is one of the genuinely difficult elements to find concentrated anywhere, and southern China holds one of the few places on Earth where it forms a deposit of its own: Lanmuchang in southwestern Guizhou, where thallium minerals occur with mercury and arsenic. The setting is that same low-temperature hydrothermal province that produced the antimony at Xikuangshan — cool fluids moving slowly through sedimentary rock, which turns out to be exactly the regime in which the soft, awkward heavy metals collect.
The full entry
For stroke order, example sentences, audio and the complete set of meanings, see the dictionary entry.
铊Thallium in the dictionary →Others built the same way
Every one of these carries 钅, and every one is a metal.