Why did Mendeleev switch the order of some elements in his periodic table, even though it contradicted their increasing atomic masses?

• A. He believed atomic number was more important than atomic mass.
• B. He wanted to arrange elements alphabetically by their names.
• C. He was following the order in which elements were discovered.
• D. He prioritized grouping elements with similar chemical properties together.

Answer: (D)

Verified step by step guidance

1. Understand that Mendeleev's periodic table was primarily organized based on increasing atomic mass, but he noticed some inconsistencies when elements did not fit well into groups with similar chemical properties.
2. Recognize that Mendeleev prioritized the chemical properties of elements over strict adherence to atomic mass order, which led him to switch the positions of certain elements to maintain groups with similar properties.
3. Recall that this decision was important because the periodic law is based on the periodic recurrence of chemical properties, not just atomic mass.
4. Note that Mendeleev's approach anticipated the modern periodic table, which is arranged by atomic number rather than atomic mass, resolving these inconsistencies.
5. Summarize that Mendeleev's priority was to group elements with similar chemical behavior together, even if it meant deviating from the order of increasing atomic mass.