(a) Did Dobereiner's triads also exist in the columns of Newlands' law of octaves? Explain your answer.
(b) What were the limitations of Dobereiner's classification of elements?
(c) What were the limitations of Newlands' law of octaves?
(a) Yes, Dobereiner's triads also existed in the columns of Newlands' law of octaves. This can be explained by taking the second column of the Newlands' classification of elements as an example. The second column has the elements lithium (Li), sodium (Na) and potassium (K), which form a Dobereiner's triad.
(b) Limitations of Dobereiner's classification of elements:
It could identify only three triads from the elements which were known at that time. It failed to arrange all the elements which were known then in the form of triads of elements with the same chemical properties.
(c) Limitations of Newlands' law of octaves:
1. Newlands' law of octaves was applicable only up to the element calcium and not beyond that, i.e, it only works for lighter elements.
2. According to Newlands, only 56 elements existed in nature and there would be no elements discovered in the future. However, this assumption was proved wrong with the discovery of several elements later on which did not fit into Newlands' law of octaves.
3. A unique slot was not given to all the elements, as Newlands put two elements which have different properties together in a single slot.
4. The element iron which resembles cobalt and nickel in its properties was given a position far away from them.
Lakhmir Chemistry 2013