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

• A. By increasing atomic mass
• B. By their 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 a property that was measurable at the time, which was atomic mass (the average mass of atoms of an element).
3. Note that Mendeleev organized elements in order of increasing atomic mass, which allowed him to observe periodic patterns in their chemical properties.
4. Understand that this arrangement helped Mendeleev predict the existence and properties of undiscovered elements by leaving gaps in his table where the pattern suggested missing elements.
5. Remember that the modern periodic table is arranged by increasing atomic number, but Mendeleev's original table was based on increasing atomic mass.