Question

Write a short note.

Mendeleev’s periodic law.

Answer 1

 Mendeleev’s periodic law.

• According to Mendeleev’s Periodic Law, “Physical and chemical properties of elements are a periodic function of their atomic masses”.
• Mendeleev classified elements according to their atomic masses and arranged these elements in increasing order of their atomic masses.
• Mendeleev classified the periodic table into horizontal rows and vertical columns. The horizontal rows are called periods, and the vertical columns are called groups. Mendeleev’s Periodic Table contains seven horizontal rows and 8 vertical columns.
• The elements with similar properties come into the same group.
• Mendeleev also left gaps in his periodic table for undiscovered elements like aluminium, silicon, and Boron in his periodic table and named them Eka-Aluminium, Eka-silicon, and Eka-Boron.
• Mendeleev not only predicted the existence of Eka-Aluminium, Eka-silicon and Eka-Boron but also described the general physical properties of these elements.
• These elements were discovered later and named Gallium, Germanium and Scandium.
• Mendeleev's periodic table could predict the properties of several elements on the basis of their position in the periodic table.
• Mendeleev's periodic table could accommodate noble gases when they were discovered.

Demerits of Mendeleev's periodic table:

• The position of isotopes could not be explained.
• The wrong order of atomic masses of some elements could not be explained.
• Position of Hydrogen could not be assigned in a periodic table.