Collie's model of benzene molecule, by Baird & Tatlock (London) Ltd., 1912-14. Wood and wire frame braced with coil springs on cast iron base.
Early 19th century chemists thought of the atoms in a molecule of an organic substance (i.e. compounds of carbon) as being associated in a more or less indefinite way. Then it was accepted that there might be groups of atoms which retained their relationship throughout many reactions. This helped to develop the theory of valency: that each atom of each element combines with a definite and characteristic number of other atoms. (This idea was implicit in Dalton's theory, but had been lost sight of. The new version was much more informative than Daltons).
One development was the idea that carbon always had a valency of 4. This explained many organic structures, carbon being linked to carbon, often in long chains, but it failed to explain the important benzene group of 6 carbon atoms. In 1865, Kekule suggested a ring structure for benzene. This was successful, but the later suggestion by Le Bel and Van't Hoff that the four valency bonds of carbon were distributed uniformly in three dimensions, while enormously extending the scope of organic structure theory, created difficulties in the case of benzene.
These models show some of the early attempts made to reconcile these theories in the case of benzene. They have been superseded by modern quantum-mechanical theories of the atom.