How was Mendeleev's periodic table originally arranged?

• A. By increasing atomic number
• B. By the number of neutrons in the nucleus
• C. By alphabetical order of element names
• D. By increasing atomic mass

Answer: (D)

Verified step by step guidance

1. Understand that Mendeleev's periodic table was created before the discovery of the atomic number and the neutron, so it could not have been arranged by these properties.
2. Recall that Mendeleev arranged elements based on their chemical properties and noticed a repeating pattern when elements were ordered by increasing atomic mass.
3. Recognize that the periodic law, as proposed by Mendeleev, states that the properties of elements are a periodic function of their atomic masses.
4. Note that Mendeleev left gaps in his table for undiscovered elements, predicting their properties based on the pattern of increasing atomic mass.
5. Conclude that the original arrangement of Mendeleev's periodic table was by increasing atomic mass, not atomic number, neutron count, or alphabetical order.