Chapter 1: Let us answer these: (Page-3)

Let us answer these: (Page-3)

Q1. What is Dobereiner's law of triads? Give one example.

Ans:  When elements are arranged in a triad in the order of increasing atomic masses, the atomic mass of the middle element was approximately equal to the arithmetic mean of the atomic masses of the other two elements. This is known as Dobereiner's law of triads.eg. This triad was made up of the alkali metals lithium, sodium, and potassium.

Triad	Atomic Masses
Lithium	6.94
Sodium	22.99
Potassium	39.1

Q2. A,B and C are the elements in Dobereiner's triad. If the atomic masses of A is 40 and that of C is 137, What would be the atomic mass of B?

Ans: According to the Dobereiner's law of triads, the atomic mass of B=40+137/2 = 177/2=88.5

Q3. What is Newland's Law of Octaves? Explain with an example.

Ans:  When the elements are arranged in increasing order of their atomic masses, the properties of the eighth element are similar to that of the first. Such classification of elements is known as  Newland's Law of Octaves.

Examples :

1. The eight element from lithium is sodium. Similarly, eight element from sodium is potassium. Lithium, sodium, potassium have similar chemical properties.

2. The eighth element from fluorine is chlorine. Fluorine and chlorine have similar chemical properties.

Q4. What are the limitations of Newland's Law of Octaves?

Ans:  Limitations of Newland’s Law of Octaves:

1.Several elements were fit into the same slots in Newland’s periodic classification. For example, cobalt and nickel were placed in the same slot.
2. Elements with dissimilar properties were grouped together. For example, the halogens were grouped with some metals such as cobalt, nickel, and platinum.
3.Newland’s law of octaves held true only for elements up to calcium. Elements with greater atomic masses could not be accommodated into octaves.

4.The elements that were discovered later could not be fit into the octave pattern. Therefore, this method of classifying elements did not leave any room for the discovery of new elements.

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