Why did Dmitri Mendeleev not use atomic number to arrange the elements in his periodic table?

• A. Atomic number values were considered unreliable due to experimental errors.
• B. The concept of atomic number had not been discovered during Mendeleev's time.
• C. He believed atomic mass was a more accurate property for organizing elements.
• D. He wanted to group elements based on their chemical reactivity rather than atomic structure.

Answer: (B)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev developed his periodic table in the late 19th century, before the discovery of the atomic number.
2. Recognize that the atomic number, which is the number of protons in an atom's nucleus, was not known or defined at that time.
3. Know that Mendeleev arranged elements primarily by increasing atomic mass because it was the most reliable and measurable property available to him.
4. Note that Mendeleev's arrangement also considered chemical properties and reactivity, which helped him predict the existence and properties of undiscovered elements.
5. Conclude that the concept of atomic number was discovered later, which eventually provided a more accurate basis for the periodic table's organization.