Development of the periodic table Transitional Reasoning Practice

Questions

1. 1.

   A student investigates historical attempts to organize chemical elements and analyzes the data for tellurium (atomic mass 127.60 u, atomic number 52) and iodine (atomic mass 126.90 u, atomic number 53). In Dmitri Mendeleev's table, tellurium was placed before iodine despite having a greater atomic mass, because grouping iodine with fluorine, chlorine, and bromine preserved their shared chemical properties. Based on this historical evidence and the subsequent development of the periodic law, which conclusion best explains why this placement proved correct in the modern periodic table?

   • A) Iodine has fewer neutrons than tellurium, which naturally reverses their atomic radii and chemical reactivity in the halogens group.
   • B) Mendeleev's original organization was completely flawed because periodic properties depend primarily on physical states at room temperature.
   • C) Moseley demonstrated that nuclear charge (atomic number) rather than atomic mass governs periodic trends, correctly ordering tellurium (52) before iodine (53).
   • D) Tellurium naturally converts into lighter isotopes under standard atmospheric conditions, resolving the discrepancy without modifying mass-based ordering.

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