MP Board · Class 10 · Science · Periodic Classification of ElementsExplain the Modern Periodic Law and discuss the main features of the Modern Periodic Table. How does it resolve the anomalies of Mendeleev's Periodic Table?

Modern Periodic Law

• Statement: The Modern Periodic Law states that 'Properties of elements are a periodic function of their atomic number.' Henry Moseley demonstrated in 1913 that atomic number is a more fundamental property of an element than its atomic mass.

Main Features of Modern Periodic Table

• Periods: There are 7 horizontal rows known as periods. Each period starts with a new shell being filled. The number of elements in a period is determined by the maximum number of electrons that can be accommodated in the shell.
• Groups: There are 18 vertical columns known as groups. Elements in the same group have the same number of valence electrons, resulting in similar chemical properties.
• Blocks: The table is divided into four blocks (s, p, d, and f) based on the subshell in which the last electron enters.

Resolution of Anomalies of Mendeleev's Periodic Table

• Position of Isotopes: Since isotopes have the same atomic number, they are placed in the same slot in the Modern Periodic Table, resolving the problem faced by Mendeleev.
• Anomalous Pairs: Elements with higher atomic masses were placed before elements with lower atomic masses in Mendeleev's table (e.g., Cobalt before Nickel) to group similar elements. By arranging according to atomic number (Co = 27, Ni = 28), this anomaly was automatically corrected.
• Electronic Configuration: It provides a clear basis for classification based on the atomic structure and electronic configuration rather than just atomic mass.