NCERT Solution for Class 10 Science Chapter 5
Periodic Classification of Elements
NCERT Books for Session 2020-2021
CBSE Board and UP Board
Intext Questions
Page No-85
Questions No-3
What were the criteria used by Mendeleev in creating his Periodic Table?
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Mendeleev’s periodic table was based on the observation that the properties of elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals.
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1. When Mendeléev started his work, 63 elements were known.
2. He examined the relationship between the atomic masses of the elements and their physical and chemical properties.
1. Among chemical properties, Mendeléev concentrated on the compounds formed by elements with
oxygen and hydrogen.
2. He selected hydrogen and oxygen as they are very reactive and formed compounds with most elements.
3. The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element for its classification.
4. He then took 63 cards and on each card he wrote down the properties of one element.
1. Mendeléev took 63 cards and on each card he wrote down the properties of one element.
2. He sorted out the elements with similar properties and pinned the cards together on a wall.
1. Mendeléev observed that most of the elements got a place in a Periodic Table and were arranged in the order of their increasing atomic masses.
2. It was also observed that there occurs a periodic recurrence of elements with similar physical and chemical properties.
Mendeléev’s Periodic Table contains:
vertical columns called ‘groups’
horizontal rows called ‘periods’
Mendeleev used atomic mass of the elements as the unique criteria of the elements. He proposed that the chemical properties of elements are the periodic function of their atomic masses. And thus, he arranged the elements in the increasing order of their atomic masses.