Which of the following best describes a key difference between Mendeleev's periodic table and Meyer's periodic table?

• A. Mendeleev left gaps for undiscovered elements and predicted their properties, while Meyer did not.
• B. Meyer arranged elements strictly by atomic number, while Mendeleev used atomic mass.
• C. Mendeleev's table included noble gases, while Meyer's table did not.
• D. Mendeleev grouped elements by their chemical reactivity, while Meyer grouped them by physical properties.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the historical context of both Mendeleev's and Meyer's periodic tables. Both scientists contributed to the development of the periodic table in the late 19th century, but their approaches had key differences.
2. Step 2: Recall that Mendeleev arranged elements primarily by increasing atomic mass and noticed patterns in their chemical properties, which allowed him to predict the existence and properties of undiscovered elements by leaving gaps in his table.
3. Step 3: Recognize that Meyer also arranged elements by atomic mass and studied their physical properties, but he did not leave gaps for undiscovered elements nor predict their properties as Mendeleev did.
4. Step 4: Note that the concept of arranging elements strictly by atomic number came later, after the discovery of the proton, so neither Mendeleev nor Meyer used atomic number as the basis for their tables.
5. Step 5: Conclude that the key difference is that Mendeleev left gaps for undiscovered elements and predicted their properties, while Meyer did not, making this the best description of their difference.