- (chemistry) The number, equal to the number of protons in an atom that determines its chemical properties. Symbol: Z
- Dutch: atoomnummer
- French: numéro atomique (or, much less often, nombre atomique )
- German: Ordnungszahl (rarely: Kernladungszahl , Atomnummer )
- Italian: numero atomico
- Spanish: níºmero atómico
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