Expert: Daniel Mazur - 11/17/2005

Question
Hi! i'm israr ahmed. i'm a student of 11th standard in pre-medical. My question s that why the atomic is denoted by 'A' & atomic number is denoted by 'Z', what is the reason behind it.

Answer
Hi Israr Ahmed,

'A' stands for Atom, Atomic. Moreover, this word is very international, it has first been used by ancient philosophers already and comes from Greek language:
'A-' ... prefix meaning negation, like English "un-", "in-", "non-"
'tomos' ... the word stem means "cut", "divide"
=>
'Atomos' ... adjective and noun meaning "indivisible"

That used to be the idea of some ancient Greek philosophers, that matter is only divisible down to some elementary particles and not beyond that. Search web resources, http://dbhs.wvusd.k12.ca.us/webdocs/AtomicStructure/Greeks.html for example, to get more details. In German language the "atomic weight" would translate as "Atomenmasse", hence the use of 'A'.

As for 'Z', it stands for the first letter in the German word 'Zahl', which is a noun meaning 'count', 'amount' or 'number' (in the sense of integer). I believe you know the atomic number Z is in essence denoting the number of electrons in anatom of a particular element. The "number of electrons" translates as "Elektronenzahl" in German. The "atomic number" translates as "Atomordnungszahl" (see the "-zahl" at the ends?). The letter 'E' has already been taken by "Energy", 'A' taken by the atomic weight, so the quantity landed with letter 'Z'.

Why does the world use it? It is because in the 19th and the beginning of the 20th century, when atomic physics experienced a real boom, German science was the world top one. Same as nowadays English is lingua franca of the world science, German was such a language in those days. It was the world wars of the 20th century that expelled most conscientious scientists to the United States and elsewhere, which ended the epoch.

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Cheers!
Daniel