Question

Short note on structure of modern periodic table?

Answer 1

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Mendeleev’s periodic table was based on atomic weight. In 1913, Moseley from his studies on X-rays found that the atomic number is the more fundamental property of an element than its atomic mass. Thus, atomic number was adopted as the basis of modern periodic table. Moseley’s periodic law was then formulated as:

The properties of an element are a periodic function of its atomic number.

The periodic table based on this law is known as the modern periodic table. This periodic table is also known as Long or Extended Form of the periodic table. In the Mendeleev’s periodic table the subgroups A and B have been kept together giving rise to short periods. In the modern periodic table, the subgroups A and B have been separated so that the periods have been extended. Therefore, the older version of the periodic table is also called the short form of periodic table and the modern periodic table is called the long or extended form of the periodic table.

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Answer 2

Features of modern periodic table:

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


A few important features of the elements present in groups are as follows:

1.The groups are not divided into subgroups.

2. The elements present in a group have the same number of valence or similar electrons.

3. The elements present in a group have the same valency.

4. The number of shells increase as we go down the group.

5. The elements present in a group have identical chemical properties.

6. The physical properties of the elements such as melting point ,boiling point, density in a group vary gradually.






Features of Periods:

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


2. The number of valence shell electrons increased by 1 unit as the atomic number increases by 1 unit on moving from left to right in a period.


3. As the number of valence shell electrons change is the chemical properties of the elements also change.

4. Different periods have different number of electrons which can be explained on the basis of filling of electrons into various shells.