Mendeleev Periodic Table: Periodic Law and Characteristics Explained with Merits and Demerits

The modern periodic table that we use today did not appear overnight. Before scientists understood atomic structure, arranging the growing number of known elements was a major challenge. As more elements were discovered, remembering their properties and relationships became increasingly difficult. In 1869, Russian chemist Dmitri Mendeleev solved this problem by creating the Mendeleev Periodic Table, a systematic arrangement of elements based on their atomic masses and chemical properties. This article describe Mendeleev’s Periodic Table, its periodic law, features and its importance in the development of chemistry. 

Table of Contents 

• What is the Mendeleev Periodic Table
• Features of the Mendeleev Periodic Table
• Merits of the Mendeleev Periodic Table
• What are the Limitations of Mendeleev Periodic Table
• Difference Between Mendeleev's Table and the Modern Periodic Table
• Frequently Asked Questions on Mendeleev Periodic Table

What is the Mendeleev Periodic Table

The Mendeleev Periodic Table is a tabular arrangement of elements in which elements are placed in the increasing order of their atomic masses and grouped according to similarities in their chemical properties.

Dmitri Mendeleev was a Russian chemist who made one of the greatest contributions to chemistry by developing the periodic table in 1869.

To organise the known elements, Mendeleev wrote the properties of each element on separate cards and arranged them repeatedly until he noticed a pattern.

He found that:

• Elements with similar properties appeared at regular intervals.
• Elements forming similar compounds could be placed in the same vertical columns.
• Atomic mass played an important role in determining periodicity.

This discovery became the basis of the Mendeleev Periodic Table.

Mendeleev observed that the properties of elements repeated periodically when arranged according to increasing atomic mass of elements. This periodic repetition of properties became the basis of his periodic table.At the time of his work, only 63 elements were known. 

Read More: Atomic Number and Mass Number

Here's what Mendeleev's Periodic Law States: 

Mendeleev proposed the following periodic law:

"The properties of elements are the periodic functions of their atomic masses."

This means that when elements are arranged according to increasing atomic masses, similar properties repeat after certain intervals.

Structure of the Mendeleev Periodic Table

The table consisted of:

• 8 groups (I to VIII)
• 7 periods

Some groups were further divided into subgroups:

• Group A
• Group B

This arrangement helped accommodate elements with similar chemical properties.

Features of the Mendeleev Periodic Table

The Mendeleev Periodic Table had several important features.

• Arrangement Based on Atomic Mass

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

Groups and Periods

• The vertical columns were called groups.
• The horizontal rows were called periods.

• Similar Elements in the Same Group

Elements having similar chemical properties were placed in the same group.

• Presence of Gaps

Mendeleev intentionally left some empty spaces in the table for elements that had not yet been discovered.

• Prediction of New Elements

The gaps allowed him to predict the properties of future elements with remarkable accuracy.

One of the greatest achievements of the Mendeleev Periodic Table was its ability to predict undiscovered elements.

Mendeleev left gaps for elements that were not known at that time and predicted their properties.

Some of these predicted elements were:

Predicted Name	Actual Element Discovered
Eka-boron	Scandium
Eka-aluminium	Gallium
Eka-silicon	Germanium

The properties predicted by Mendeleev matched closely with those of the newly discovered elements, proving the accuracy of his periodic table.

Merits of the Mendeleev Periodic Table

1. Systematic Arrangement of Elements

It provided a scientific method for arranging elements according to their properties.

2. Prediction of Undiscovered Elements

Mendeleev successfully predicted several unknown elements and their properties.

3. Correction of Atomic Masses

The positions of some elements helped scientists correct their atomic masses.

4. Grouping of Similar Elements

Elements with similar chemical behaviour were placed together.

5. Foundation of the Modern Periodic Table

The Mendeleev Periodic Table became the basis for the development of the modern periodic table.

What are the Limitation of Mendeleev Periodic Table

Although highly successful, the table had certain limitations.

1. Uncertain Position of Hydrogen:Hydrogen showed similarities with both Group 1 and Group 17 elements, so its position remained uncertain.

2. Position of Isotopes:Isotopes have different atomic masses but identical chemical properties. According to Mendeleev's arrangement, they should occupy different positions, which was impossible.

3. Anomalous Pairs of Elements:Some elements had to be placed against the increasing order of atomic mass.

Examples:

• Argon and Potassium
• Cobalt and Nickel
• Tellurium and Iodine

4. No Explanation of Atomic Structure:The table could not explain why periodicity existed.

5. Irregular Increase in Atomic Mass:The increase in atomic masses was not always uniform.

Difference Between Mendeleev's Table and the Modern Periodic Table

Basis	Mendeleev Periodic Table	Modern Periodic Table
Basis of Arrangement	Atomic mass	Atomic number
Number of Groups	8	18
Position of Isotopes	Not explained	Explained properly
Position of Hydrogen	Uncertain	Special position
Noble Gases	Not included initially	Included as Group 18
Periodic Law	Based on atomic mass	Based on atomic number

Read More: 118 Elements their Symbols and Atomic Numbers 

Till now we have learned the Mendeleev Periodic Table was one of the most important milestones in the history of chemistry. The Mendeleev Periodic Table laid the foundation for the modern periodic table and remains one of the greatest scientific achievements in chemistry.