How did Henry Moseley change the periodic table in 1913 to its modern form?

• A. He arranged the elements by increasing atomic number instead of atomic mass.
• B. He introduced the concept of electron shells.
• C. He grouped the elements based on their chemical reactivity.
• D. He classified elements into metals, nonmetals, and metalloids.

Answer: (A)

Verified step by step guidance

1. Understand that before Henry Moseley's work, the periodic table was primarily arranged by increasing atomic mass, which sometimes led to inconsistencies in element placement.
2. Recognize that Henry Moseley used X-ray spectroscopy to study the frequencies of X-rays emitted by elements, discovering a relationship between these frequencies and the positive charge in the nucleus.
3. Learn that Moseley defined the concept of atomic number as the number of protons in an atom's nucleus, which is unique for each element and determines its identity.
4. See how Moseley's work showed that arranging elements by increasing atomic number, rather than atomic mass, resolved previous inconsistencies and better reflected the elements' chemical properties.
5. Conclude that Moseley's rearrangement of the periodic table by atomic number is the basis for the modern periodic table, improving its predictive power and organization.