Page 57 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

E L E M E N T S I R-3.4

The right lower position of an atomic s ymbol is reserved for an index (subscript) indicating
the number of such atoms in a f ormula. For e xample, S 8 is the formula o f a m olecule
containing eight sulfur atoms (see Section IR-3.4). For formalisms when oxidation states
or charges are also shown, see Section IR-4.6.1.

Example:

S
1. 32 2þ represents a d oubly i onized sulfur atom of atomic number 16 and mass
16
number 32.
4
The nuclear reaction between 26 Mg and He nuclei to yield 29 Al and H 1 1 n uclei is written
12
13
2
3
as follows :
26 29
Mgða; pÞ Al
For the use of atomic symbols to indicate i sotopic modification in chemical formulae and the
nomenclature of isotopically modified compounds see Section IR-4.5 and Chapter II-2
of Ref. 4 r espectively.

IR-3.3 I S O T O P E S

IR-3.3.1 Isotopes of an element

The isotopes of an element all bear the same n ame (but see Section IR-3.3.2) and are
designated by mass n umbers (see Section IR-3.2). For example, the atom of atomic number
8 a nd mass number 18 is named oxygen-18 and has the symbol 18 O.

IR-3.3.2 Isotopes of hydrogen
1
Hydrogen is an exception to the rule in Section IR-3.3.1 in that the three isotopes H, H 2 a nd
3
H c an have the alternative names protium, deuterium and tritium, respectively. The
symbols D a nd T m ay be used for deuterium and tritium but H 2 a nd H 3 a re preferred because
D a nd T c an disturb t he alphabetical ordering i n f ormulae (see Section IR-4.5). The
combination of a m uon and an electron behaves l ike a l ight isotope of hydrogen and is
named muonium, symbol Mu. 5
1
1
These names give rise to the names proton, deuteron, triton and muon for the cations H ,
2 1 3 1 1
H , H and Mu , r espectively. Because t he name proton is often used in contradictory
1
1
senses, i.e. f or isotopically pure H ions on the one hand, and for the naturally occurring
undifferentiated isotope mixture on the other, it is recommended that the undifferentiated
mixture be designated generally by the name hydron, d erived from hydrogen.

IR-3.4 E L E M E N T S ( o r e lementary substances)

IR-3.4.1 Name of an element of indefinite molecular formula or structure

A s ample of an element that has an undefined f ormula, or is a m ixture of allotropes (see
Sections IR-3.4.2 to IR-3.4.5), bears t he same name as the atom.

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