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Class 10  »  Chemistry  »  Periodic Classification of Elements

Early Classification Attempts Dobereiner Newlands - UNSOLVED PRACTICE SET

Class 10

Chapter: Periodic Classification of Elements | Topic: Early Classification Attempts Dobereiner Newlands

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Class 10

EARLY CLASSIFICATION ATTEMPTS DOBEREINER NEWLANDS - UNSOLVED PRACTICE SET

Topic: Early Classification Attempts Dobereiner Newlands

Time: 40 mins | Marks: 30 | Difficulty: Medium

Multiple Choice Questions

Q1. Who proposed the concept of triads in the classification of elements?

  1. Newlands
  2. Mendeleev
  3. Dobereiner
  4. Moseley

Q2. In Dobereiner's triad, the atomic mass of the middle element is approximately:

  1. The sum of the atomic masses of the other two elements
  2. The average of the atomic masses of the other two elements
  3. Twice the atomic mass of the first element
  4. Half the atomic mass of the third element

Q3. Which of the following is an example of a Dobereiner triad?

  1. Li, Na, K
  2. H, He, Li
  3. C, N, O
  4. Fe, Co, Ni

Q4. Newlands arranged the known elements in order of increasing:

  1. Atomic number
  2. Atomic mass
  3. Valency
  4. Density

Q5. Newlands' Law of Octaves was applicable only up to which element?

  1. Oxygen
  2. Calcium
  3. Iron
  4. Chlorine

Q6. The main limitation of Newlands' classification was that:

  1. He arranged elements by atomic number
  2. He assumed every eighth element had similar properties, which was not true for heavier elements
  3. He only considered metals
  4. He ignored the concept of atomic mass

Short Answer Questions

Q7. State Dobereiner's Law of Triads. Give one example of a triad identified by him.

Q8. What was Newlands' Law of Octaves? Why did he compare elements to musical notes?

Q9. List any two limitations of Dobereiner's classification of elements.

Q10. Why was Newlands' Law of Octaves rejected by the scientific community? Mention any two reasons. 

Q11. Your music teacher explains that musical notes repeat every eighth note (sa, re, ga, ma, pa, dha, ni, sa). Newlands used a similar idea for elements. Explain how Newlands applied this musical concept to chemistry, and why it eventually failed for heavier elements.

Q12. Dobereiner could identify only three triads among the known elements. What does this tell us about the usefulness of his system? 

Long Answer Questions

Q13. Compare Dobereiner's Triads and Newlands' Octaves on the following basis:

(a) Basis of classification

(b) Number of elements considered

(c) Success rate and limitations

(d) Contribution to the development of the modern periodic table

Which of the two was more successful, and why?

Q14. Describe the work of Johann Wolfgang Dobereiner in classifying elements. How did he group elements? Why was his system considered a stepping stone towards the modern periodic table? Illustrate with the example of the lithium-sodium-potassium triad.

Q15. Imagine you are a scientist in the 1860s reviewing Newlands' paper on the Law of Octaves. He claims that cobalt and nickel should be placed in the same slot because they have similar properties, and he groups iron with sulphur and phosphorus.

(a) What scientific criticism would you raise about placing cobalt and nickel together?

(b) Why is grouping iron with sulphur and phosphorus chemically incorrect?

(c) Despite these flaws, what valuable insight did Newlands provide that helped future scientists?

(d) Why did the scientific community initially refuse to publish his work?

Numerical / Application-Based Problems

Q16. Dobereiner observed that in a triad of elements A, B, and C, the atomic mass of element B is approximately the average of A and C.

(a) If element A has an atomic mass of 7 u and element C has an atomic mass of 39 u, calculate the expected atomic mass of element B.

(b) Name the actual element that fits this triad.

(c) Why did Dobereiner's triads work for some elements but not for others?

Q17. Newlands arranged the first 56 elements (known at that time) in order of increasing atomic mass.

(a) If the atomic mass of lithium is 7 u and sodium is 23 u, predict the atomic mass of the eighth element after lithium according to Newlands' Law of Octaves.

(b) Does this element actually have similar properties to lithium? Explain.

(c) Calculate the average atomic mass of the elements in Dobereiner's triad: chlorine (35.5 u), bromine (80 u), and iodine (127 u). Does bromine fit as the middle element?

Q18. A student is trying to classify the following elements using Dobereiner's triads:

Set 1: Be (9 u), Mg (24 u), Ca (40 u)

Set 2: N (14 u), P (31 u), As (75 u)

(a) Check whether Set 1 forms a valid Dobereiner triad by calculating the average atomic mass.

(b) Check whether Set 2 forms a valid Dobereiner triad.

(c) What conclusion can you draw about the limitations of Dobereiner's system from these calculations?


Total: 30 Marks | Time: 40 mins

Explore more topics in Periodic Classification of Elements

Mendeleevs Periodic Table Merits and Limitations Modern Periodic Table Moseley Periods and Groups Trends in the Periodic Table Atomic Size Metallic Character Valency across Periods and Groups Metals Non Metals and Metalloids in the Table