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