Mendeleev’s periodic table, modern periodic table

Mendeleev’s Periodic Table

1. Proposed by Dmitri Mendeleev in 1869.
2. Based on the periodic recurrence of properties of elements when arranged in order of increasing atomic mass.
3. Contained 63 known elements at the time.
4. Mendeleev organized elements into rows and columns to form the periodic table.
5. He left gaps in the table for undiscovered elements and predicted their properties accurately, such as gallium (eka-aluminum) and germanium (eka-silicon).
6. Grouped elements with similar properties together in vertical columns, called groups.
7. Highlighted periodicity, the repeating pattern of properties across rows called periods.
8. Some anomalies were present due to arranging elements strictly by atomic mass (e.g., iodine and tellurium).
9. Laid the foundation for the modern periodic table by emphasizing the importance of periodic trends.
10. Did not consider noble gases as they were undiscovered during his time.

Modern Periodic Table

1. Developed after the discovery of the atomic number by Henry Moseley in 1913.
2. The modern periodic table is based on the periodic law, which states that the properties of elements are periodic functions of their atomic numbers.
3. Arranges elements in order of increasing atomic number rather than atomic mass, resolving anomalies in Mendeleev's table.
4. Consists of 7 periods (horizontal rows) and 18 groups (vertical columns).
5. Groups are further divided into:
   • Main groups: Groups 1, 2, and 13-18 (s and p block elements).
   • Transition elements: Groups 3-12 (d block elements).
   • Inner transition elements: Lanthanides and actinides (f block elements).
6. Includes the discovery of noble gases and their placement in Group 18.
7. Predicts properties of new elements based on their position in the table.
8. Allows the study of periodicity in properties such as atomic radius, ionization energy, and electron affinity.
9. Elements in the same group exhibit similar chemical and physical properties due to the same number of valence electrons.
10. The position of elements reflects their electronic configuration.
11. Groups 1 and 17 contain highly reactive elements, while Group 18 contains inert gases.

Key Differences Between Mendeleev's and Modern Periodic Table

1. Mendeleev’s table was based on atomic mass, while the modern table is based on atomic number.
2. The modern table resolves anomalies such as the placement of iodine and tellurium.
3. Includes noble gases and the lanthanide and actinide series.
4. Provides a systematic way to understand periodicity in chemical properties.

Applications of the Periodic Table

1. Helps predict the properties of elements and their compounds.
2. Guides the discovery of new elements.
3. Used to explain chemical reactions and bonding trends.
4. Facilitates the study of periodic trends like ionization energy, electronegativity, and atomic size.
5. Provides a framework for understanding the behavior of metals, non-metals, and metalloids.
6. Widely used in fields like chemistry, biology, physics, and material science.

Key Points

1. Mendeleev’s periodic table was revolutionary but had some limitations.
2. The modern periodic table, based on atomic numbers, resolved those limitations.
3. Periodic trends help predict the reactivity and stability of elements.
4. Understanding the periodic table is essential for success in competitive exams.