How did Dmitri Mendeleev organize 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 that Dmitri Mendeleev's original periodic table was an early attempt to organize elements based on their properties before the discovery of atomic number.
2. Recognize that Mendeleev arranged the elements primarily by increasing atomic mass, which was the best available quantitative property at the time.
3. Note that while arranging by atomic mass, Mendeleev also grouped elements with similar chemical properties into columns, creating a pattern of periodicity.
4. Be aware that Mendeleev left gaps in his table predicting the existence and properties of undiscovered elements, showing the predictive power of his organization.
5. Contrast Mendeleev's method with the modern periodic table, which is organized by increasing atomic number rather than atomic mass.