Question 10

Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.

Answer

Mendeleev’s periodic table	Modern periodic table
1. Elements are arranged in the increasing order of their atomic masses.	1. Elements are arranged in the increasing order of their atomic numbers.
2. There are a total of 7 groups (columns) and 6 periods (rows).	2. There are a total of 18 groups (columns) and 7 periods (rows).
3. Elements having similar properties were placed directly under one another.	3. Elements having the same valence shell are present in the same period while elements having the same number of valence electrons are present in the same group.
4. The position of hydrogen could not be explained.	4. Hydrogen is placed above alkali metals.
5. No distinguishing positions for metals and non-metals.	5. Metals are present at the left hand side of the periodic table whereas non-metals are present at the right hand side.

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