Category CHEMICAL_FORMULA

Name:
'CHEMICAL_FORMULA'

Parent category:
CHEMICAL

Definition:

   
     The CATEGORY of data items which specify the composition and chemical
     properties of the compound. The formula data items must agree
     with those that specify the density, unit-cell and Z values.
 
     The following rules apply to the construction of the data items
     _chemical_formula.analytical, *.structural and *.sum. For the
     data item *.moiety the formula construction is broken up into
     residues or moieties, i.e. groups of atoms that form a molecular
     unit or molecular ion. The  rules given below apply within each
     moiety but different requirements apply to the way that moieties
     are connected (see _chemical_formula.moiety).
 
     1. Only recognized element symbols may be used.
 
     2. Each element symbol is followed by a 'count' number. A count of
    '1' may be omitted.
 
     3. A space or parenthesis must separate each cluster of (element
    symbol + count).
 
     4. Where a group of elements is enclosed in parentheses, the
    multiplier for the group must follow the closing parentheses.
    That is, all element and group multipliers are assumed to be
    printed as subscripted numbers. [An exception to this rule
    exists for *.moiety formulae where pre- and post-multipliers
    are permitted for molecular units].
 
     5. Unless the elements are ordered in a manner that corresponds to
    their chemical structure, as in _chemical_formula.structural,
    the order of the elements within any group or moiety
    depends on whether or not carbon is present. If carbon is
    present, the order should be: C, then H, then the other
    elements in alphabetical order of their symbol. If carbon is
    not present, the elements are listed purely in alphabetic order
    of their symbol. This is the 'Hill' system used by Chemical
    Abstracts. This ordering is used in _chemical_formula.moiety
    and _chemical_formula.sum.
 
       _chemical_formula.iupac      '[Mo (C O)4 (C18 H33 P)2]'
       _chemical_formula.moiety     'C40 H66 Mo O4 P2'
       _chemical_formula.structural '((C O)4 (P (C6 H11)3)2)Mo'
       _chemical_formula.sum         'C40 H66 Mo O4 P2'
       _chemical_formula.weight      768.81

Category is of type Set