Development of the periodic table Transitional Reasoning Download PDF

Questions

1. 1.

   When Dmitri Mendeleev organized elements by increasing atomic mass, he encountered anomalies such as tellurium ($127.6\text{ amu}$) and iodine ($126.9\text{ amu}$), which he had to reverse to keep them in families with matching chemical behaviors. Decades later, Henry Moseley examined the characteristic X-ray emission spectra of various elements bombarded with high-energy electrons. Based on this historical transition, which statement accurately explains how Moseley's work resolved these classification discrepancies?

   • A) Moseley demonstrated that atomic mass fluctuates because of unstable valence shells, requiring elements to be ordered by their neutron-to-proton ratios.
   • B) Moseley proved that chemical periodicity depends primarily on the total mass of neutrons in the nucleus rather than the arrangement of electrons.
   • C) Moseley showed that the true organizing property of the elements is nuclear charge (atomic number), which places tellurium ($Z = 52$) naturally before iodine ($Z = 53$).
   • D) Moseley established that elements in the same vertical column must possess identical total counts of subatomic particles to exhibit similar reactivities.