Development of the periodic table Original Scenario-Based Practice

Questions

1. 1.

   During a chronotemporal research expedition to St. Petersburg in 1869, an archivist observes Dmitri Mendeleev arranging cards representing known chemical elements into columns and rows. The archivist notices that Mendeleev occasionally breaks the numerical sequence of atomic weights and intentionally leaves blank cards with question marks scattered across the grid. Which statement correctly explains the scientific reasoning behind Mendeleev's organizational method and these deliberate gaps?

   • A) He organized elements strictly by atomic number and left spaces for isotopes that had not yet been isolated.
   • B) He prioritized recurring chemical properties over rigid atomic mass order, predicting that the gaps corresponded to undiscovered elements with predictable characteristics.
   • C) He grouped elements exclusively by their valence electron configurations, leaving spaces where specific electron subshells were unfilled.
   • D) He arranged elements strictly by increasing density, leaving spaces solely where laboratory measurement errors were suspected.

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