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 雷 léi 'thunder'.
Where you actually meet it
镭射 / 鐳射 (léishè) — laser (Hong Kong and Singapore usage; Taiwan says 雷射, the mainland says 激光)
The element itself
Radium had to be extracted from tonnes of pitchblende residues to yield a fraction of a gram, a labour of years carried out in a leaking shed, and the reward was a substance that glows faintly blue in the dark of its own accord. That glow made it briefly fashionable — in paint, in tonics, in cosmetics — before its effects on the people who worked with it became undeniable and the industry collapsed. Chemically it behaves like calcium, which is exactly the problem.
Where it sits among the 118
First isolated in 1898.
In living things
Radium is chemically calcium's heavy cousin — same group, same charge, similar chemistry — and the body, which has no way to tell them apart, files it into bone. That is the whole of its biological story and the reason it was so damaging: an alpha emitter deposited permanently in the skeleton irradiates the marrow at point-blank range. The lesson was learned from the women who painted luminous watch dials in the 1920s and were taught to point their brushes with their lips, and the studies that followed them became the foundation of how internal radiation dose is thought about.
The full entry
For stroke order, example sentences, audio and the complete set of meanings, see the dictionary entry.
镭Radium in the dictionary →Others built the same way
Every one of these carries 钅, and every one is a metal.