In what order did Dmitri Mendeleev arrange the elements in his original periodic table?

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

Answer: (D)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev created the first widely recognized periodic table in 1869, aiming to organize elements based on their properties.
2. Recall that Mendeleev arranged elements primarily by increasing atomic mass, which was the best available measure at the time to reflect periodic trends.
3. Recognize that arranging by atomic number was not possible then because the concept of atomic number was developed later, in the early 20th century.
4. Note that Mendeleev's arrangement also grouped elements with similar chemical properties into columns, highlighting periodicity.
5. Therefore, the correct order Mendeleev used was by increasing atomic mass, not alphabetical order, atomic number, or chemical reactivity.