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Periodic Classification of Elements — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10SciencePeriodic Classification of Elements5 Marks
Question
  1. Why do we classify elements?
  2. What were the two criteria used by Mendeleev in creating his Periodic Table?
  3. Why did Mendeleev leave some gaps in his Periodic Table?
  4. In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
  5. Would you place the two isotopes of chlorine Cl- 35 and Cl- 37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
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Answer

  1. To make the understanding of properties of elements and compounds simpler/To make order out of chaos.
  2. The criteria used by Mendeleev in creating his periodic table:
  1. He arranged the elements on the basis of their increasing atomic masses.
  2. He put elements of similar properties in a group.
  1. To make sure that elements with similar properties lie in the same group, Mendeleev left some gaps in the periodic table. These gaps were left for subsequent inclusion of the elements not known at that time. The elements were discovered later.
  2. There was no mention of noble gases like helium, neon and argon as they were not known at that time and were discovered much later.
  3. Same slot because their chemical properties are same.

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