After Mendeleev organized the periodic table by atomic weight, what major change did Henry Moseley introduce to improve its accuracy?

• A. He arranged the elements by atomic number instead of atomic weight.
• B. He organized the table by increasing density of the elements.
• C. He classified elements according to their electron configurations.
• D. He grouped elements based on their chemical reactivity.

Answer: (A)

Verified step by step guidance

1. Understand the historical context: Mendeleev originally arranged the periodic table based on increasing atomic weight, which sometimes led to inconsistencies in element placement.
2. Recognize the problem: Some elements did not fit well when ordered strictly by atomic weight, causing confusion in predicting properties and element groups.
3. Learn about Moseley's contribution: Henry Moseley used X-ray spectra to determine the atomic number of elements, which corresponds to the number of protons in the nucleus.
4. Identify the key change: Moseley rearranged the periodic table by increasing atomic number rather than atomic weight, which resolved inconsistencies and better reflected chemical properties.
5. Conclude that this change improved the accuracy and predictive power of the periodic table by aligning element order with fundamental atomic structure.