How does the arrangement of elements in the modern periodic table differ from that of Mendeleev's periodic table?

In Mendeleev's periodic table, elements were arranged according to their atomic masses. He also left gaps in the table for undiscovered elements, and even predicted some of their properties. This enabled the periodic table to be a useful tool in predicting the properties of elements and their compounds, as well as in the discovery of new elements.

In the modern periodic table, elements are arranged according to their atomic numbers (which represent the number of protons in the nucleus), rather than their atomic masses. This is based on the principle that the properties of elements are periodic functions of their atomic numbers. The modern periodic table consists of groups (columns) and periods (rows) which help classify elements based on their chemical and physical properties.

The differences between Mendeleev's periodic table and the modern periodic table are: 1. Basis of arrangement: Mendeleev based his periodic table on atomic masses, while the modern periodic table is based on atomic numbers. 2. Periodic law: Mendeleev's periodic law stated that the properties of elements are a periodic function of their atomic masses, while the modern periodic law states that the properties of elements are a periodic function of their atomic numbers. 3. Position of isotopes: In Mendeleev's periodic table, isotopes (elements with the same atomic number but different atomic masses) would be placed in separate positions due to their different atomic masses. In the modern periodic table, isotopes occupy the same position since they have the same atomic number. 4. Prediction of undiscovered elements: Mendeleev predicted the existence and properties of undiscovered elements, leaving gaps in his periodic table. The modern periodic table does not predict new elements, but its organization allows for the discovery of new elements to be added according to their atomic numbers. 5. Structure: The modern periodic table includes additional groups and periods, as well as the division of elements into blocks (s, p, d, and f) based on their electron configuration.

To conclude, the main differences between the arrangement of elements in the modern periodic table and Mendeleev's periodic table are the basis of arrangement (atomic masses vs. atomic numbers), the periodic law, the position of isotopes, the prediction of undiscovered elements, and the overall structure of the tables. The modern periodic table has a more accurate and comprehensive classification system, which makes it a superior tool for understanding the chemical and physical properties of elements.