By paying constant heed to this matter of the affinities,
chemists are able to make diagrammatic pictures of the plan of
architecture of any molecule whose composition is known. In the
simple molecule of water (H2O), for example, the two hydrogen
atoms must have released each other before they could join the
oxygen, and the manner of linking must apparently be that
represented in the graphic formula H--O--H. With molecules
composed of a large number of atoms, such graphic representation
of the scheme of linking is of course increasingly difficult,
yet, with the affinities for a guide, it is always possible. Of
course no one supposes that such a formula, written in a single
plane, can possibly represent the true architecture of the
molecule: it is at best suggestive or diagrammatic rather than
pictorial. Nevertheless, it affords hints as to the structure of
the molecule such as the fathers of chemistry would not have
thought it possible ever to attain.


PERIODICITY OF ATOMIC WEIGHTS

These utterly novel studies of molecular architecture may seem at
first sight to take from the atom much of its former prestige as
the all-important personage of the chemical world. Since so much
depends upon the mere position of the atoms, it may appear that
comparatively little depends upon the nature of the atoms
themselves. But such a view is incorrect, for on closer
consideration it will appear that at no time has the atom been
seen to renounce its peculiar personality. Within certain limits
the character of a molecule may be altered by changing the