Practice assignment – 2
Chapter - 5
QUESTIONS:- (1 mark each)
Q1. What is meant by classification of elements?
Q2. What was the limitation of Dobereiner law of triads?
Q3. Why do Li, Na and K how resemblance on the basis of Dobereiner’s law of triads?
Q4. Classify the following elements according to the Law of Octaves:
K, Na, Ca, S, O, P, Al
N, F, Si, C, Cl, Mg
Q5. A, B and C are elements of Dobereiner’s triad. If the atomic mass of A is 7 and that of C s 23, what will be the atomic mass of B.
Q6. Classify the following elements into groups of triads
Cl, Ca, Ba, Sr, K, Li, Br, I, Na
Q7. Na and K resemble in their properties, how many elements are there between them?
Q8. State Mendeleev’s law.
Q9. Mendeleev classified the elements on the basis of two factors. What were these two factors?
Q10. What is meant by ‘groups’ of Periodic Table?
Q11. What is meant by periodicity of properties?
Q12. Name two elements whose valencies are equal to their group number.
Q13. What are the elements of group 1 and group 17?
Q14. Which one has the bigger size?
Na (11) or Cl (17), Cl (17) or F (9)
Q15. What would be the nature of oxides formed by the element on the left hand side of the periodic table? Give one example.
Q16. How many shells are present in the elements of 3rd period? Give reason also.
Q17. An element ‘X’ has atomic number 20. To which group and period does it belong?
Q18. Find the atomic number of the element whose electronic configuration is 2, 8, 5.
Q19. Arrange the following elements increasing order of their atomic radii:
Li, Be, F, N
Cl, At, Br, I
Q20. Out of Li and K, which will have stronger metallic character and why?
Q21. Write the number of horizontal rows in the modern periodic table. What are these rows called?
Q22. Give the number of elements in 2nd and 5th period in Modern Periodic Table.
Answers
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Answer:
1.Elements can be classified as metals, metalloids, and nonmetals, or as a main-group elements, transition metals, and inner transition metals.
2.) All the known elements then could not be arranged in the form of triads . 2) The law failed for very low mass or for vary high mass elements . 3) AS the techniques improved for measuring atomic masses accurately , the law was unable to remain strictly valid .
Explanation:
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