An atom is the smallest unit of a chemical element that still has that element’s properties, made of a nucleus with electrons around it.
It comes from Greek *atomos*, meaning 'uncuttable', from *a-* 'not' and *temnein* 'to cut'. Ancient philosophers used it for the idea of a smallest possible piece of matter.
Ironically, atoms turned out to be very 'cuttable'—we’ve split them into protons, neutrons, and electrons, and even smaller particles. But the ancient guess that matter is built from tiny building blocks was so good that we kept their word for our modern version.
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