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Question:

The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all three attempts.

Solution:

Dobereiner's Triads:

  • Advantage: Successfully grouped elements with similar properties into triads, showing a pattern in atomic weights and properties.
  • Limitation: Applicable only to a limited number of elements; many elements did not fit into triads.

Newland's Law of Octaves:

  • Advantage: Suggested a periodic relationship between elements, with properties repeating every eighth element (similar to musical octaves).
  • Limitation: Worked well only for lighter elements; the pattern broke down for heavier elements. It also forced dissimilar elements into the same group.

Mendeleev's Periodic Table:

  • Advantage: Arranged elements based on increasing atomic weights and recurring chemical properties, leaving gaps for undiscovered elements which were later found and their properties matched his predictions.
  • Limitation: Some elements were placed out of order of atomic weight to maintain the correct chemical family grouping; this was later explained by the concept of isotopes and a better understanding of atomic structure (atomic number).