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

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

Answer: (A)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev created the periodic table in the 19th century before the discovery of the atomic number concept.
2. Recognize that Mendeleev arranged elements based on their properties and noticed a repeating pattern when elements were ordered by increasing atomic mass.
3. Note that Mendeleev left gaps in his table for elements that were not yet discovered, predicting their properties based on the pattern of increasing atomic mass.
4. Distinguish that the modern periodic table is arranged by increasing atomic number, but Mendeleev's original table was arranged by increasing atomic mass.
5. Conclude that the correct way Mendeleev arranged the elements was by increasing atomic mass, which allowed him to group elements with similar chemical properties together.