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

• A. By increasing atomic number
• B. By increasing atomic mass
• C. By arranging elements alphabetically
• D. By grouping elements according to their chemical reactivity

Answer: (B)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev created the first widely recognized periodic table in the 19th century, before the discovery of the atomic number.
2. Recall that Mendeleev arranged elements based on a property that was measurable at the time, which was the atomic mass (also called atomic weight).
3. Recognize that Mendeleev noticed patterns in the properties of elements when they were listed in order of 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 initial organization was by increasing atomic mass, not atomic number or alphabetical order, and that he grouped elements according to their chemical reactivity as a secondary step.