Which feature of Mendeleev's periodic table was considered particularly ingenious?

• A. He classified elements according to their melting points.
• B. He arranged elements strictly by increasing atomic number.
• C. He grouped elements based on their color.
• D. He left gaps for undiscovered elements and predicted their properties.

Answer: (D)

Verified step by step guidance

1. Understand the historical context: Mendeleev's periodic table was created before the discovery of atomic numbers and many elements, so he had to rely on known properties of elements to organize them.
2. Recognize that Mendeleev arranged elements primarily by increasing atomic mass, but more importantly, he noticed patterns in their chemical properties that repeated periodically.
3. Identify the key innovative feature: Mendeleev left intentional gaps in his table where no known elements fit the pattern, predicting that these gaps corresponded to undiscovered elements.
4. Note that Mendeleev went further by predicting the properties of these missing elements based on the trends in the table, which was a bold and ingenious scientific approach.
5. Conclude that this predictive power and the use of gaps to accommodate unknown elements distinguished Mendeleev's periodic table from other classification attempts.