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Chapter 5 Periodic Classification of Elements Solutions

Question - 21 : - How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Answer - 21 : - The number of valence electrons decides an atomтАЩs position in the periodic table while the electronic configuration decides the number of valence electrons.

Question - 22 : - In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38.

Answer - 22 : - Which of these have physical and chemical properties resembling calcium?

Answer
Calcium has an atomic number of 20, and thus has an electronic configuration of 2, 8, 8, 2. Thus, calcium has 2 valence electrons. The electronic configuration of the element having atomic number 12 is 2, 8.2. Thus, this element with 2 valence electrons resemble calcium the most.

Question - 23 : - Compare and contrast the arrangement of elements in MendeleevтАЩs Periodic Table and the Modern Periodic Table.

Answer - 23 : -

MendeleevтАЩs Periodic Table

Modern Periodic Table

Elements are arranged in the increasing order of their atomic masses.

Elements are arranged in the increasing order of their atomic numbers.

There are 8 groups

There are 18 groups

Each groups are subdivided into sub group тАШaтАЩ and тАШbтАЩ

Groups are not subdivided into sub-groups.

Groups for Noble gas was not present as noble gases were not discovered by that time

A separate group is meant for noble gases.

There was no place for isotopes.

This problem has been rectified as slots are determined according to atomic number.

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