PERIODIC TABLE ( CHEMISTRY)

. PERIODIC TABLE (CHEMISTRY)

*  Mendeleev's periodic law (1863)

" The physical and chemical properties of elements are periodic function of thier atomic weights."

*  Modern periodic table law (1913)

" The physical and chemical properties of the elements are a periodic function of their atomic number."

*  Features of modern periodic table

• It has 7 horizontal raws called periods and 18 vertical columns called group or families.
• The first period is the shorted period consisting of 2 elements.
• The second and third periodic contain 8 elements, fourth and fifth periods contains 18 elements, sixth period contain 32 elements and seventh period is now complete with discovery of elements 113,115,117 and118.
• The elements of second period are known as  bridge elements.
• The elements of I, II, XIII, XV, XVI, XVII and XVIII groups are collectively known as normal or representative element.
• The element of XVIII group are known as inert gases or noble gases. 
• The element of III group to XII group are known as transition elements. This is because their properties lia between the properties of the reactive metals ( alkali and alkaline metal)placed on extreme left and the non metals (halogens and chalcogens=oxygen family) placed on extreme right of the periodic table. Their general electronic configuration is (n-1)

• the series of elements with Z = 58 to Z = 71 which occur in periodic table after lanthanum are called lanthanides or lanthanoids. The series of elements with Z = 90 to Z = 103 which occur in the periodic table after actinum are called actinides or actinoids

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