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MCAT Question A Day - 10/18/14 - Answer!

In 1869 both Mendeleev and Meyer. working separately. published nearly identical classification schemes for the elements that were the forerunners of the modern periodic table. Although scientists of that time had no knowledge of atomic numbers, both schemes ordered the elements in nearly correct order from lowest to highest atomic number. Which of the following is the most likely explanation?

A.  Both scientists noticed similar patterns in chemical and physical behaviors among the elements.
B.  Atomic number generally increases with atomic weight and the scientist knew the atomic weights of the elements.
C.  The chemical identity was predictable from the number of valence electrons which was known at the time.
D.  Although the number of protons for each element was not known, the number of neutrons was.

B is correct. We are looking for an answer that would allow for the prediction of the order of atomic number. If atomic number increases with atomic weight, the scientists could have made accurate predictions.

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