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Chapter 9: Problem 5

Mendeleev's periodic table did not preclude the possibility of a new group of elements that would fit within the existing table, as was the case with the noble gases. Moseley's work did preclude this possibility. Explain this difference.

Short Answer

Expert verified
The main difference between Mendeleev's and Moseley's periodic tables lies in their organizing principles and how they accommodated new elements. Mendeleev's table, arranged by atomic mass, anticipated and made room for undiscovered elements. Moseley's table, arranged by atomic number, precluded the possibility of new groups of elements. Instead, new elements simply extend the existing periods, fitting sequentially based on their atomic number.

Step by step solution

01

Understand Mendeleev's Periodic Table

Dmitri Mendeleev, a Russian chemist, formulated the Periodic Law and created a periodic table of elements in the 19th century. He arranged elements in order of increasing atomic mass and noticed that certain properties of elements were repeated after certain intervals. Remarkably, Mendeleev also left blank spots in his table for elements that had yet to be discovered, correctly predicting their properties. Therefore, his method did not rule out the possibility of finding new groups of elements that would fit within the existing table.
02

Understand Moseley's Contribution

Henry Moseley, an English physicist, conducted X-ray experiments which led to a significant improvement of the periodic table. He found that Atomic Number, not Atomic Mass, was the correct basis for arranging elements, solving anomalies in Mendeleev's table where atomic masses did not fit the observed periodicity. Moseley's work confirmed the Periodic Law and made it possible to assign every element a specific place in the periodic table based on its atomic number. As such, Moseley's work led to the current understanding of the periodic table where no new group of elements could be inserted without disrupting the existing order.
03

Explain the Difference

The main difference between Mendeleev's and Moseley's approach involves the organizing principle of their tables and how they handled potential new elements. Mendeleev's table was primarily arranged by atomic mass and left room for undiscovered elements. In contrast, Moseley refined the table by organizing it by atomic number, which precluded the possibility of inserting a new group of elements. New elements can be discovered, but they will simply extend the existing periods, taking a sequential place in the periodic table based on their atomic number, rather than forming new groups within it.

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Most popular questions from this chapter

Compare the elements \(\mathrm{Na}, \mathrm{Mg}, \mathrm{O},\) and \(\mathrm{P}.\) (a) Place the elements in order of increasing ionization energy. (b) Place the elements in order of increasing electron affinity.

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