Short Answer

The first periodic table was created by Dmitri Ivanovich Mendeleev in 1869. He arranged the known chemical elements in order of increasing atomic mass and grouped them based on similar chemical properties.

Mendeleev’s table allowed him to predict the existence and properties of undiscovered elements, making it a powerful tool for chemistry. His work laid the foundation for the modern periodic table, which is now arranged by atomic number.

Detailed Explanation :

Mendeleev’s Contribution

Dmitri Mendeleev, a Russian chemist, developed the first systematic periodic table while studying the properties of elements. He observed that when elements were arranged by increasing atomic mass, their chemical and physical properties repeated periodically.

• Periodic Law (Mendeleev’s version): The properties of elements are a periodic function of their atomic masses.
• He left gaps in the table for elements that were yet to be discovered, predicting their properties based on patterns in the table.

Structure of the First Periodic Table

1. Rows (Periods): Elements were arranged horizontally in order of increasing atomic mass.
2. Columns (Groups): Elements with similar chemical properties were placed in the same vertical column.
3. Gaps for Undiscovered Elements:
   • Mendeleev predicted the existence of gallium (eka-aluminium), germanium (eka-silicon), and scandium (eka-boron).
   • When these elements were discovered, their properties closely matched his predictions.

Significance of Mendeleev’s Table

1. Prediction of New Elements:
   • His table correctly predicted atomic masses, chemical properties, and densities of missing elements.
2. Systematic Organization:
   • Grouped elements with similar properties, helping chemists study patterns in chemistry.
3. Foundation for Modern Periodic Table:
   • Modern periodic law is based on atomic number, but Mendeleev’s concept of periodicity remains central.
4. Educational Tool:
   • The table is widely used to teach chemistry and study elemental properties.

Examples of Predictions

• Eka-silicon (Germanium): Predicted density 5.5 g/cm³, actual 5.35 g/cm³
• Eka-aluminium (Gallium): Predicted melting point 30°C, actual 29.8°C
• Eka-boron (Scandium): Predicted properties matched the discovered element

Comparison with Modern Periodic Table

• Mendeleev arranged elements by atomic mass, while the modern table arranges by atomic number (Z).
• Some elements like iodine and tellurium were swapped in Mendeleev’s table to maintain property grouping.
• The modern periodic table retains periods and groups but uses atomic number for precise arrangement.

Other Early Contributions

• Before Mendeleev, other chemists like Dmitri Dobereiner (triads) and John Newlands (law of octaves) noticed patterns, but Mendeleev’s table was comprehensive and predictive.
• His work proved that periodicity could guide scientific discovery.

Impact on Chemistry

1. Provided a systematic method to organize elements.
2. Allowed chemists to predict missing elements and their properties.
3. Formed the basis for modern chemistry, research, and industrial applications.
4. Demonstrated that atomic structure determines chemical behavior, linking chemistry and physics.

Conclusion

The first periodic table was created by Dmitri Mendeleev in 1869, arranging elements by increasing atomic mass and grouping them by similar chemical properties. His table allowed the prediction of undiscovered elements, demonstrated periodic patterns, and laid the foundation for the modern periodic table. Mendeleev’s work is considered one of the most important contributions to chemistry, shaping how scientists understand and study elements today.