question_answer 3)

What were the limitations of Newlands' Law of Octaves?                

Answer:

The major limitations of Newlands' law of octaves were :                  (i) It was applicable to only lighter elements having atomic masses upto 40 u, i.e., upto calcium. After calcium, the first and the eighth element did not have similar properties. For example chromium (Cr) and yttrium (Y) are the first and the eighth element placed in the same column but they have entirely different properties.      (ii) It was assumed that only 63 elements existed in nature and no new elements would be discovered in the future. But later on several new elements were discovered whose properties did not fit into the law of octaves.                                             (iii) Some similar elements have been separated from one another while some dissimilar elements have been placed in the same column. For example, iron (Fe) resembles cobalt (Co) and nickel (Ni) but has been placed far away from these elements. Similarly cobalt and nickel do not resemble halogens (F, CI, Br) but have been placed in the same column.       (iv) When noble gases were discovered, the properties of the eighth element were no longer similar to the first one. Actually, now it was the first and the ninth element which has similar properties.