Modern Periodic Table


 
 
Concept Explanation
 

Modern Periodic Table

Modern periodic table: In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property and on the basis of this, he modified Mendeleev’s periodic law as “physical and chemical properties of the elements are a periodic function of their atomic number”. This is called modern periodic law. When the elements were arranged in the increasing order of the atomic number, the obtained table is called modern periodic law.

Features of Modern Periodic Table:

This table has 18 vertical columns, known as groups and 7 horizontal rows, known as periods.

Features of Groups:

  •   The groups are not divided into sub-groups.
  •   The elements present in a group have the same number of valence or similar electrons.
  •   The elements present in a group have the same valency.
  •   The number of shells increases as we go down the group.
  •   The elements present in a group have identical chemical properties.
  •   The physical properties of the elements such as melting point, boiling point, density in a group vary gradually.
  • Features of Periods:

  •  Elements of a period do not have the same number of valence electrons but they contain the same number of shells.
  • The number of valence shell electrons increases by one unit as the atomic number increases by one unit on moving from left to right in a period. Therefore, the atoms of different elements with same number of shells are placed in the same period.
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    Sample Questions
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    Question : 1

    Which of the following are correct :

    (a) Elements of a period do not have the same number of valence electrons but they contain the same number of shells.

    (b) In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property.

    (c) As the number of valence shell electrons changes, the chemical properties of the elements also change.

    Right Option : D
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    Question : 2

    Which of the following are correct :

    (a) In Modern Periodic Table groups are not divided into sub-groups.

    (b) In Modern Periodic Table elements present in a group have the same number of valence or similar electrons.

    (c) In Modern Periodic Table elements present in a group have the same valency.

    Right Option : D
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