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Periodic Table and Periodicity in Properties

NIOS · Class 12 · Chemistry

Quick revision notes for Periodic Table and Periodicity in Properties — NIOS Class 12 Chemistry. Key concepts, formulas, and definitions for last-minute revision.

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Key Topics to Revise

1

Early Attempts at Classification of Elements

  • Dobereiner's Triads (1817): Elements grouped in sets of three where the atomic weight of the middle element is approximately the arithmetic mean of the other two. Example: Li (6.94), Na (22.99), K (39
  • Limitation of Dobereiner's Triads: Could only classify a few elements; insufficient data on atomic weights at that time.
  • Newlands' Law of Octaves (1863): Elements arranged in increasing order of atomic weights; every eighth element had similar properties to the first — like musical octaves (sa, re, ga...). Example: Li a
2

Mendeleev's Periodic Table

  • Mendeleev (1869) arranged elements in increasing order of atomic weights and grouped elements with similar chemical properties in the same vertical column (group).
  • Mendeleev's Periodic Law: 'The properties of elements are periodic functions of their atomic weights.'
  • Mendeleev's table had 8 groups (I to VIII) and several periods.
3

Modern Periodic Law and Long Form of the Periodic Table

  • Moseley (1913) discovered that atomic number (number of protons) is the fundamental property of an element, not atomic weight. He changed the basis of the periodic table.
  • Modern Periodic Law: 'The properties of elements are periodic functions of their atomic numbers.'
  • This solved all the defects of Mendeleev's table — isotopes got the same place (same atomic number), and anomalous pairs like Co-Ni were correctly arranged.
4

IUPAC Nomenclature for Elements with Atomic Number > 100

  • For elements with atomic number greater than 100 (and specifically used for > 103), IUPAC (1994/1997) developed a systematic naming system to avoid naming disputes.
  • Numerical roots used: 0=nil, 1=un, 2=bi, 3=tri, 4=quad, 5=pent, 6=hex, 7=sept, 8=oct, 9=enn.
  • Rule: Write the roots for each digit of the atomic number in order, then add 'ium' at the end.

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Full Notes

Key Concepts

Dobereiner discovered that certain elements couldJohn Newlands arranged elements in orderDmitri Mendeleev arranged elements by increasingIn 1913The modern periodic table perfectly matches

Frequently Asked Questions

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