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MATTER / ATOMS AND MOLECULES / STRUCTURE OF THE ATOM / CHEMICAL REACTIONS AND EQUATIONS / ACIDS, BASES AND SALTS / METALS AND NON-METALS / CARBON AND ITS COMPOUNDS / PERIODIC CLASSIFICATION OF ELEMENTS
After as Dobereiner’s Traids was ruled out, an English chemist J.A.R. Newlands observed similarities in physical and chemical properties of every eighth element when he arranged the then known elements in the increasing order of their atomic masses. He compared this with the octaves found in musical scale. Therefore, this concept is known as Newlands’ Law of Octaves.
“When elements are arranged in the order of their increasing relative atomic masses, the properties of eighth element were similar to the first one like the eighth note of a musical scale.”
(a) Li (1st element ) , Na (8th element from Li) and K (8th element from Na) show similar properties.
(b) Be (1st element ) , Mg (8th element from Be) and Ca (8th element from Mg) posses same properties.
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Significance of Newlands’ Law of Octaves
- It was the first logical attempt to classify elements on the basis of increasing order of their atomic masses.
- Periodicity (a regular interval) of every eighth elements was recognized for the first time.
Even though, this law was failed for the following reasons –
- This classification could be best applied up to the element calcium. The feature of resemblance of properties of the eighth element when arranged in the increasing order of their atomic mass was not successfully followed by the elements having atomic masses higher than calcium.
- At the time of Newlands , only 56 elements were known. When more new elements were discovered after giving this classification, e.g. noble gases (He, Ne, Ar etc.) they could not be accommodated in to the octave structure.
- In order to fit elements in the table –
(a) two elements were put in to the same slot, e.g. Co and Ni ; Ce and La etc.
(b) elements of dissimilar properties were kept in the same note,
(i) Co and Ni show completely different properties from F, Cl and Br , but they all were kept in one note.
(ii) Ce and La possess different properties from Cr and Y, but are placed in same column.
(c) Elements having similar characteristics were placed at different places.
e.g. – Iron (Fe) shows resemblance with Co and Ni in properties, was placed far away.
Thus, Newlands’ Law of Octaves worked properly with lighter elements or upto calcium only.