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NCERT Solutions for Class 10th Science


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Chapter 5. Periodic Classification of Elements

Chapter Review




Chapter Review:

  • Groups having three elements each. So he called these groups called triads.
  • According to Dobereiner's Traids "The order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements".
  • According to Newlands’ Law of Octaves "Every eighth element repeat the properties of the first element".
  • Newlands’ Law of Octaves worked well with lighter elements only.
  • When Mendeleev started work on Periodic Table, oniy 63 elements were known.
  • The Modern Periodic Table has 18 vertical columns known as ‘groups’
    and 7 horizontal rows known as ‘periods’.
  • The Modern Periodic Law state that ‘Properties of elements are a periodic function of their atomic number.’
  • The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.
  • The atomic size may be visualised as the distance between the centre of the nucleus and the outermost shell of an isolated atom.
  • The atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.
  • Boron, silicon, germanium, arsenic, antimony, tellurium and polonium are intermediate in properties and are called metalloids or semi   metals.


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