How did Dmitri Mendeleev organize the elements in his original periodic table?

• A. By increasing atomic number
• B. By alphabetical order
• C. By increasing atomic mass
• D. By their chemical reactivity

Answer: (C)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev created the first widely recognized periodic table in 1869, before the discovery of the atomic number.
2. Recall that Mendeleev arranged elements based on a property that was known at the time and could be measured for all elements: atomic mass.
3. Recognize that Mendeleev noticed patterns in the properties of elements when they were ordered by increasing atomic mass, which allowed him to group elements with similar chemical properties together.
4. Note that Mendeleev left gaps in his table for elements that were not yet discovered, predicting their properties based on the trends in atomic mass and chemical behavior.
5. Conclude that Mendeleev's original periodic table was organized by increasing atomic mass, not atomic number or alphabetical order.