Mendeleevs Periodic Table Merits and Limitations - UNSOLVED PRACTICE SET

Q7. State Mendeleev's Periodic Law. What was the basis of his classification?

Q8. Name the two elements whose properties were predicted by Mendeleev before their discovery. What names did he give them?

Q9. Why did Mendeleev reverse the order of tellurium (atomic mass 127.6 u) and iodine (atomic mass 126.9 u) in his periodic table? 

Q10. List any two limitations of Mendeleev's periodic table.

Q11. Your grandfather's old chemistry textbook shows Mendeleev's periodic table with elements like eka-boron and eka-aluminium. When you look at a modern periodic table, you find these elements exist today as scandium and gallium. Explain how Mendeleev's predictions proved the power of his periodic table. 

Q12. Why was the position of hydrogen problematic in Mendeleev's periodic table?

Q13. Describe the construction of Mendeleev's periodic table. Explain how he arranged elements and why he left gaps. Discuss any three merits of his table that made it superior to earlier classification systems.

Q14. Compare Mendeleev's periodic table with the modern periodic table on the following basis:

(a) Basis of classification

(b) Position of isotopes

(c) Position of noble gases

(d) Position of transition elements

Why was Mendeleev's table eventually replaced by the modern periodic table?

Q15. During a school project, you are asked to create a model of Mendeleev's periodic table using cards representing elements.

(a) How would you arrange the cards? What property would you use to order them?

(b) You notice that cobalt (atomic mass 58.9 u) comes before nickel (atomic mass 58.7 u) in the table. Why did Mendeleev place them this way despite the atomic mass order?

(c) Where would you place the element with properties similar to both alkali metals and halogens? Why is this placement difficult?

(d) What would you do with elements like lanthanum and cerium that seem to have very similar properties?

Q16. Mendeleev predicted the properties of an element he called "eka-silicon" (later discovered as germanium). He predicted its atomic mass would be about 72 u and its density about 5.5 g/cm³.

(a) When germanium was actually discovered, its atomic mass was found to be 72.6 u and density 5.35 g/cm³. Calculate the percentage error in Mendeleev's prediction for atomic mass.

(b) Why was Mendeleev able to predict properties so accurately?

(c) Name the element below germanium in the same group. Predict its approximate atomic mass using Mendeleev's logic.

Q17. In Mendeleev's periodic table, elements were arranged in horizontal rows called periods and vertical columns called groups.

(a) If an element X has an atomic mass of 40 u and shows properties similar to calcium (atomic mass 40 u), but Mendeleev placed another element Y (atomic mass 39 u) before it in the same group, explain why Mendeleev might have done this.

(b) Calculate the average atomic mass of the elements in the triad: calcium (40 u), strontium (88 u), and barium (137 u). Does strontium fit as the middle element of a Dobereiner triad?

(c) Why did Mendeleev prefer grouping by properties over strict atomic mass order?

Q18. A student is analyzing Mendeleev's original periodic table and finds the following elements in Group VIII:

Fe (55.8 u), Co (58.9 u), Ni (58.7 u)

(a) Why did Mendeleev place these three elements together in the same group despite their different atomic masses?

(b) Calculate the average atomic mass of iron and nickel. Is it close to cobalt's atomic mass?

(c) What modern concept explains why these three elements have similar properties?