How to Write 氘 (dāo) — Meaning “deuterium”

Imagine a knife (刀) slicing through a cloud of gas (气) to separate out heavy hydrogen — that’s deuterium. The "knife" sound (dāo) matches the character’s pronunciation exactly. Think of it as "gas with a knife" for its role in splitting atoms.

Write the left radical 气 first: horizontal stroke, then the three-stroke hook (like a sideways "3"), and finally the bottom stroke. Then add 刀: start with the top hook, then the slash. A common mistake is making the 气 hook too short or forgetting that 刀’s hook angles inward. Total 6 strokes.

气 (qì) is the radical meaning "gas" by itself, while 氘 adds 刀 to create the specific element deuterium. 氕 (piē) is the character for protium (ordinary hydrogen), using 气 with a single slash (丿). Visually, 氘 has a knife shape inside, 氕 has a simple stroke, and 气 has no added element. Only 氘 refers to heavy hydrogen.

氘 appears mainly in scientific contexts like chemistry and nuclear physics, for example in 氘灯 (deuterium lamp) used in laboratory equipment or 氘核 (deuteron) in particle research. It is not part of daily vocabulary or HSK lists. When reading about nuclear fusion or heavy water, 氘 is the key term for deuterium.

Common words containing 氘 include: 氘气 (dāo qì) — deuterium gas; 氘核 (dāo hé) — deuteron; 氘灯 (dāo dēng) — deuterium lamp.