After Lewis, the chemical formulas, which were developed starting with the
mass equivalents of elements, have gained another meaning. Now, bonding lines
between the symbols of elements became the symbols for the electron pairs.
is the same as the formula H-H
This symbolism is also shown for the molecules of methane and etene:
Since in some molecules, as for example in the molecule of ammonia, two of
electrons are not included in covalent bonds, Lewis has introduced the category of
nonbonding electrons, or the lone electron pairs. In the following figure, the
electronic structure of ammonia is represented with the lone electron pair above the
symbol of nitrogen atom.
Facsimile of Lewis
representations of
interlinking of atoms
modelled as cubes with
electrons in vertices
126
12 Limits of Structural Theory