Formulae and Graphics

Both representations (e) or (f) of unsaturated rings are used in this text. In the case of linear molecules containing formal multiple bonds, equal electron sharing is sometimes implied by using broken lines as (d) rather than localised (c) (see Chapter 3). 

Several different representations of the orthophosphate anion PO are in use, for example, (a) and (b) (see Section 5.33). The representation of the phosphoryl linkage as P=0 has become more or less standard, although it is generally agreed, that in some circumstances other representations may be more appropriate (Sections 3.16 and 5.33). 

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These readers will need to keep in mind the special (now archaic) senses in which such terms as "atomicity," "diatomic," "equivalent," "rational formula," and "graphic formula" were used in the middle of the nineteenth century. These historical senses are explained in the text. 

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