these structural types are not the representations of molecular structure in modern
sense, they were an important step in the development of chemical theory. This
could clearly be seen from the symbolism by which the types are drawn from the
knowledge about substitution reactions:
On the right side of the curly bracket are atoms or groups replaceable in substitution reaction. The structural type is in this substitution preserved. In modern
symbolism these types could be represented in following way:
Structural types
Type HCl
HCl, NaCl, KBr,…
Type H 2 O
H 2 O, H 2 S, (CH 3 ) 2 Se, Na 2 O, ..
Type NH 3
NH 3, (CH 3 ) 2 NH 2, PH 3, ..
Type CH 4
CH 4, CH 2 Cl 2, SiCl 4, ..
10 Systematization, Classification, Structure, and Elements
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