Multiple Choice
Which statement best describes the nature of most new elements added to the periodic table in the last hundred years?
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2. Atoms & Elements
Periodic Table: Classifications
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Why did early scientists arrange the periodic table by atomic mass rather than atomic number?
A
Atomic numbers were not yet discovered or understood.
B
Atomic mass was considered less important than atomic number.
C
Atomic number was identical for all elements.
D
Elements were classified based on their chemical reactivity only.
Verified step by step guidance1
Understand the historical context: Early scientists did not have knowledge of the atomic number, which is the number of protons in an atom's nucleus.
Recognize that atomic mass, which is the weighted average mass of an element's isotopes, was measurable through experiments available at the time.
Since atomic number was unknown, scientists used atomic mass as the primary property to organize elements in the periodic table.
Note that atomic number was later discovered and understood to be the fundamental property that defines an element, leading to the modern arrangement of the periodic table.
Conclude that the reason early periodic tables were arranged by atomic mass is because atomic numbers were not yet discovered or understood.
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