Why did Mendeleev leave blank spaces in his version of the periodic table?

• A. He wanted to separate metals from nonmetals more clearly.
• B. He predicted the existence of undiscovered elements that would fit those spaces.
• C. He was unsure about the arrangement of known elements and left spaces for future corrections.
• D. He believed some elements did not belong in the periodic table.

Answer: (B)

Verified step by step guidance

1. Understand the historical context: Mendeleev was developing the periodic table in the 19th century when not all elements were discovered yet.
2. Recognize that Mendeleev arranged elements by increasing atomic mass and noticed recurring chemical properties, leading to the periodic law.
3. Identify that Mendeleev left blank spaces intentionally in his table where no known elements fit the observed patterns of properties.
4. Interpret these blank spaces as predictions for elements that had not yet been discovered but were expected to exist based on the trends in the table.
5. Conclude that Mendeleev's blank spaces demonstrated his confidence in the periodic law and his ability to predict properties of undiscovered elements.