How well did the periodic system match actual chemical data at the time of its formulation? Here you can observe the evolution of the periodic system as new elements and compounds were discovered across the nineteenth century.
This site is a supplement to 10.1073/pnas.2119083119. We invite you to read the full article.
The collection of known substances conforms the Chemical Space. Two elements are similar inasmuch as they combine in similar ways e.g. Na and K are quite similar since they both make compounds of the form XCl, X2SO4, XN3, etc. In chemical jargon, we say that these elements are substitutable. The groups of the System of Chemical Elements make sense inasmuch as they comprise widely substitutable elements.
In the graph below you can follow the evolution of the Chemical Space across the nineteenth century, from the perspective of the commonalities exhibited by the elements. Shift-click some elements to retrieve their viable substitutions.
We measure similarity of element A to element B as the percentage of compounds of A where it can be substituted by B i.e. as the probability of A being substitutable by B in a compound. Note the asymmetry of the relation.
In the graph below each arrow A→B indicates that A is most similar to B. Hover an arrow for detailed information. Click on an element to see all its similarities.
Nineteenth century's uncertainty concerning atomic weights is expected to impact the System of Chemical Elements. We developed an algorithm that transforms contemporary chemical formulae to fit any given atomic weights, within a degree of tolerance that accounts for experimental error.
Select a nineteenth century chemist and a tolerance to retrieve the similarities he wouldd have seen through the lenses of the atomic weights that he adopted.