Which two elements on the periodic table would have been placed in different groups in Moseley's periodic table but not in Mendeleev's?

Answer 1

Let us be quite clear about this -- Mendeleev's Periodic Table (1871 version) was perfectly accurate.There were two or three anomalies in it. Tellurium was placed in a group with selenium and sulfur leaving iodine to go with bromine and chlorine. Mendeleev spent 20 years arguing (falsely) that the experimentally determined atomic weight of tellurium had to be wrong. Nickel and cobalt were assigned identical atomic weights to allow nickel to be put in a family with palladium and platinum, and cobalt with rhodium and iridium. There was evidence at the time that nickel was slightly lower on the atomic weight scale, but Mendeleev's assignment of atomic weights was within the experimental error. And finally argon and potassium were hugely out of order on the atomic weight scale, because it was very obvious that argon was a noble gas and potassium an alkali metal. But argon was only discovered in 1894, and Mendeleev was reluctant to even accept the noble gases as elements, let alone deal with that particular anomaly.

So the atomic number scale that was uncovered by Moseley's work cleared up these anomalies, but did not lead to any changes in the periodic table.