Book of the Week: The Periodic Table: Its Story and Significance

Orga­niz­ing the chem­i­cal ele­ments into reg­u­larly recur­ing cat­e­gories was a major step in the his­tory of chemisty. The Russ­ian chemist Mendeleev played an impor­tant role in cre­at­ing the mod­ern peri­odic table, and look­ing at how he got there pro­vides some ideas for orga­niz­ing, clas­si­fy­ing, and ana­lyz­ing large data sets.

The Periodic Table, Eric Scerri, Oxford University Press 2007.

The Peri­odic Table, Eric Scerri, Oxford Uni­ver­sity Press 2007.

First, the ideas around peri­od­ic­ity evolved over time. Sci­en­tists like Lavoisier, John Dal­ton, Prout, and Dobere­iner con­tributed ideas around the ele­ments and their proer­ties. Dobere­iner dis­cov­ered that cer­tain groups of ele­ments — eg stron­tium oxide had approx­i­mately the same weight as the aver­age of the weights of bar­ium oxide and cal­cium oxide.

In for­mula:

SrO = CaO + BaO/​2107 = (59 + 155)/2

The three ele­ment groups (Sr, Ca, Ba) are called tri­ads. Oth­ers are Br, Cl, I (Bromium, Clorine, Iodine). The Ger­man sci­en­tist Johann Gmelin devel­oped an arrange­ment of ele­ments by tri­ads as follows:

Johann Gmelin's arrangement of chemical elements based on triads.

Johann Gmelin’s arrange­ment of chem­i­cal ele­ments based on triads.

A key fac­tor in devel­op­ing the peri­odic table was good data. In 1860, Stanis­lao Can­niz­zaro pub­lished a paper with a con­sis­tent table of atomic weights of the then known ele­ments for the Karl­sruhe Con­fer­ence, the first world­wide con­fer­ence on chemisty. The avail­abil­ity of good data (and a pre­dic­tive method for new ele­ments) facil­i­tated the arrange­ment by periods.Meneleev’s cre­ation of the peri­odic table has tra­di­tion­ally been ascribed to hav­ing writ­ten ele­ment and atomic weight on small cards (like index cards) that he arranged on a desk­top into peri­ods. In 1869, he wrote a ver­sion of the peri­odic table on the back of an enve­lope, which he later refined.Looking at the process, hav­ing a phys­i­cal manip­u­la­tive (cards) and a phys­i­cally writ­ten orga­ni­za­tion (dia­gram on the back of an enve­lope), facil­i­tated dis­cov­er­ing the order in the peri­odic table.At one point in my career I used to pub­lish an annual data book with charts, data tables ‚and analy­sis around cloud ser­vices. To do it I cre­ated a pro­to­type page and cut up each data table, graph, sum­mary, and analy­sis sec­tion. We sat and reor­ga­nized the paper cutouts unti we found a pat­tern that told the story behind the data and uncov­ered the most insights. Some­thing about shuf­fling paper and mark­ing it up worked bet­ter than try­ing to do every­thing on the screen.

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