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Lesson: History of the Periodic Table

Worksheet • 4 Questions


During the early 1800s, scientists attempted to understand the chemical elements by sorting them. Which property of the elements was used to order them?

  • ARelative atomic mass
  • BMelting point
  • CAtomic number
  • DReactivity
  • EDensity


Periodic tables have been around for a couple of hundred years, and some of them look very different from the one we have today. What is it about periodic tables that makes them periodic?

  • AThey group elements based on their behaviors, which repeat periodically from the lighter to the heavier elements.
  • BThey arrange elements in reference to their reactivity with iodine—they are per-iodic.
  • CThey are tables of information that are periodically updated to reflect our current knowledge.
  • DThey organize elements based on their periods of radioactivity.
  • EThey have rows as well as columns.


Mendeleev’s periodic table was used to predict the existence of many unknown elements. Which term best describes the role of the periodic table in these predictions?

  • ATheory
  • BLaw
  • CHypothesis
  • DObservation
  • EModel


Dmitri Mendeleev developed the first periodic table to allow for elements yet to be discovered. Why did he leave gaps where others did not?

  • AHe grouped elements by their behavior and left a gap if no known element fit his model.
  • BHe made his original table unnecessarily large by including duplicates of certain elements.
  • COthers knew about more elements than Mendeleev, so they were able to fill the gaps.
  • DHe thought that it was more important that the table looked attractive, so he left artistic spaces.
  • EHe was forgetful and missed some of the elements.