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> Have a look at the heading under "Gruppe." It's the formula of the element's oxide. According to the Periodic Videos video (linked from another comment), the
by quietbritishjim 8y ago
> Have a look at the heading under "Gruppe." It's the formula of the element's oxide.
According to the Periodic Videos video (linked from another comment), the reason those are there is to justify splitting the list of elements into rows in those particular places. The reasoning today is to do with eletron shells (I'm not a chemist but I presume that electron shells are also the root cause of those formulae) but at the time periodic table was created electrons hadn't yet been discovered!
- apo 8y agoYou are right (slaps forehead), and I was not thinking about the historical context. The earliest tables were based on "valence", or the ratio with which an element tended to combine with other elements in compounds. Two of the most consistent and easily obtained compounds are those of hydrogen and oxygen, which nearly always combine with other "monovalent" elements in ratios of 1 and 2, respectively. When a new element was discovered, the ratios with which it formed oxides and hydrides could be determined, and this would allow its placement on the table. A student from the late 1800s would only be able to think in terms of equivalents, not electrons and their orbitals - as you point out. The inclusion of hydride and oxide formula templates would have been an integral part of using the table.