Question

Explain Mendeleev's periodic table. [4 Makers]​

Answer 1

Answer:

(a) Mendeleev arranged all the 63 known elements in increasing order of their atomic masses

(b)the table consists of vertical columns called groups and horizontal rows called periods

(c) the elements with similar physical and chemical properties came under the same groups

(d) he could not assign a correct position to hydrogen in the periodic table

Answer 2

Introduction :

• At the time when Mendeleev give his periodic table, 63 elements were known.
• Mendeleev arranged these elements in increasing order of their atomic masses in horizontal rows now called periods in such a way that elements with similar properties fell under the same vertical columns called group.
• Mendeleev's original periodic table was published in a German journal in 1872.

Characteristic features :

• There are 7 horizontal rows called periods. They are numbered from 1 to 7.
• There are eight vertical columns called groups.
• The elements which lie on left hand side of each group constitutes sub group A are called Normal or Representative elements.
• The elements which lie on right hand side of each group constitutes subgroup B and are called as Transition elements.
• Noble gases were not known at the time of Mendeleev.
• Therefore, there was no group of noble gases in Mendeleev's original periodic table.
• However, when these gases were discovered around the year 1900 and new group called the zero group was added to the Mendeleev's periodic table.