Which unique approach did Dmitri Mendeleev take when constructing his periodic table?

• A. He left gaps for undiscovered elements and predicted their properties.
• B. He classified elements according to their color.
• C. He arranged elements strictly by increasing atomic number.
• D. He grouped elements based solely on their physical states at room temperature.

Answer: (A)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev developed the periodic table in the 19th century before the discovery of atomic numbers and many elements.
2. Recognize that Mendeleev arranged elements primarily by increasing atomic mass, but he noticed patterns in their chemical properties that repeated periodically.
3. Identify that 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 unique and bold approach at the time.
5. Contrast this with other methods: arranging by color, physical state, or strictly by atomic number were not Mendeleev's approaches, as atomic number was discovered later.