the.com/atomic number

means The count of protons in an atom's nucleus — the single number that determines which element it is.

from 'Atomic' traces back to Greek 'atomos' (uncuttable), coined by philosophers imagining matter's smallest piece — ironic, since we later split it anyway. 'Number' comes from Latin 'numerus.' The specific concept of 'atomic number' as proton count emerged in the early 20th century, when Henry Moseley's X-ray experiments (1913) showed that elements line up by nuclear charge rather than atomic weight, fixing the periodic table's true order.