Aug 142012

As we know, chemistry is one of the most important branches of science which deals with the composition, properties and transformation of any substance. In other words, it can be defined as the branch of science which studies different elements, compunds, radicals, their nature etc. These days, chemistry has became so vast and advanced that we can find innumerable number of new and unknown terminologies. These types of terminologies are widely used in the field of chemistry. One of such terminologies is Mendeleev’s periodic table.

Introduction to Mendeleev’s Periodic Table

We can find about 109 elements in this world. Among them 92 elements are natural elements and 17 elements are artificial elements. It is nearly impossible to study the physical and chemical properties of these elements individually. Therefore, to make the study of those physical and chemical properties easier and scientific, a Russian scientist named Dmitri Mendeleev gave birth to a law which is known as Mendeleev’s Periodic Law.

This law states that, “The physical and chemical properties of the elements are the periodic functions of their atomic mass or weight.” This means that, if the elements are arranged on the basis of their increasing atomic weight, similar properties will be repeated after certain interval.

On the basis of this Mendeleev’s periodic law, Mendeleev’s periodic table was developed. Mendeleev’s periodic table consists of groups and periods. The vertical columns are called groups whereas the horizontal rows are called periods.

There are altogether nine groups which are group I, II, III, IV, V, VI, VII, VIII and group 0. Each group from group I to group VII are divided into sub-groups, namely sub-group A and sub-group B. The elements which belong to sub-group A have certain characters different than the elements which belong to sub-group B. The group 0 contains inert or noble elements whose valencies are 0.

Periods: Periods are the horizontal rows in the periodic table. There are altogether seven periods in the table and these periods can be classified as short period, long period and very long period.

1. Short period: Short period can be divided into first, second and third periods. First period consists of two elements whereas second as third periods consist of eight elements each.

2. Long period: Long period can be classified in fourth and fifth periods which consist of eighteen elements each.

3. Very long period: This period can further be divided into sixth and seventh period. The sixth period consists of 32 elements, including Lanthanides whereas the seventh period consists of 32 elements theoretically but practically it consists of only 19 elements. So, it is called incomplete period.

Anomalies/Demerits of Mendeleev’s Periodic Table

1. In Mendeleev’s periodic table, hydrogen is present in group IA but its characteristics are also similar to the elements lying is group VIIA. It means that it can be placed in both groups I and VII. Therefore, in Mendeleev’s periodic table, the position of hydrogen is not clear.

2. In the Mendeleev’s periodic table, the elements are arranged on the basis of their increasing atomic weights, Hydrogen has three isotopes, i.e. it has got three atoms with different atomic weights. So, it needs three positions. But it has not been separated in the periodic table.

3. Copper and Mercury have similar chemical properties but they are placed in different groups in Mendeleev’s periodic table. Copper is placed in group IB whereas Mercury is placed in group IIB.

4. Copper, Gold and Silver have different chemical properties but they are placed under same group, i.e. group IB.

5. Fourteen Lanthanides and fourteen Actinides have not been separated and given proper place in Mendeleev’s periodic table. They are placed in two horizontal rows below the periodic table.

Though Mendeleev’s periodic table has brought out a new revolution in the classification of elements, it is not used currently because of the defects found in it. Instead of it, a new periodic table named Modern Periodic Table is being used which follows the modern periodic law.