2. Mendeleev's Periodic Table

Periodic classification of elements

Sample paper

1. What is the mendeleev periodic law?
2. What is modern periodic law?
3. What is the name given to the horizontal rows and vertical column
4. What are the drawbacks of the mendeleev periodic law
5. How many groups and periods are found in the mendeleev periodic law
6. Why noble gases are not present in the mendeleev periodic table
7. How many groups and periods are found in the long form of table
8. What is ionization enthalpy why the second ionization enthalpy of alkali metals is greater than the first ionization enthalpy
9. Why the atomic radius of chlorine is less than atomic radius of sodium
10. What is electronegativity how does electronegativity variates in periodic table from moving top to bottom
11. Why hydrogen is placed at the top of the periodic table
12. Who discover the atomic number
13. What are diagonal elements
14. What is electron affinity how does it changes when we move from left to right in the periodic table
15. Why noble gases do not react with any other elements

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Mendeleev’s Periodic Table

Mendeleev’s Periodic Law:

Physical and chemical properties of elements are the periodic function of their atomic masses.
Mendeleev’s periodic table is based on the chemical properties of elements.
Mendeleev’s periodic table contains vertical columns called ‘groups’ and horizontal rows called ‘periods’.
Achievements of Mendeleev’s Periodic Table: 63 elements were known at the time of classification.

• Elements with similar properties could be grouped together.
• Mendeleev left some gaps in his periodic table. Mendeleev boldly predicted the existence of some elements that had not been discovered at that time.
• Noble gases discovered, could be placed without disturbing the existing order.

Remember
Scandium, gallium and germa-nium have properties similar to Eka-boron, Eka-aluminium and Eka-silicon respectively.

Limitations of Mendeleev’s Classification

• The position of hydrogen in the table was not certain because it could be placed in the group of alkali metals as well as in halogens.
• Isotopes of elements were placed in the same position in the table though according to their atomic masses, they should have been placed in different positions.
• Certain elements of higher atomic mass proceed those with lower atomic mass. For example, tellurium (atomic mass 127.6) precedes iodine (atomic mass 126.9). Iodine was placed after tellurium though it had lower atomic mass because Iodine had properties similar to bromine and not selenium.