atom

https://doi.org/10.1351/goldbook.A00493
Smallest particle still characterizing a @C01022@. It consists of a @N04256@ of a positive charge (\(Z\) is the @A00499@ and \(e\) the @E02032@) carrying almost all its mass (more than 99.9%) and \(Z\) electrons determining its size.
Source:
Red Book, 3rd ed., p. 35 [Terms] [Book]