Question

Write Newlands’ law of octaves for classification of elements.

Answer 1

Hint: Think about what the word ‘octaves’ means and how it may be related to the first 3 periods of the Modern Periodic Table. Consider the number of elements that had been discovered till the 19th century.

Complete step by step solution:
The classification of elements proposed by J.A.R. Newlands in 1865 was considered somewhat of a breakthrough in chemistry. Although some people had attempted to classify elements which would help determine the properties of new elements, Newlands’ method of classification was the first one in which some kind of periodicity was seen.
Newlands arranged all the elements that had been discovered then in the order of increasing atomic weight (relative to hydrogen). He then observed that every eighth element, in that order, seemed to resemble the first element chemically and physically. So, he proposed the ‘Law of Octaves’. It states that:

“If chemical elements are arranged in the order of increasing atomic weight, then elements having similar physical and chemical properties can be seen after an interval of every seven elements.”

Newlands’ Octaves
H	Li	Be	B	C	N	O
F	Na	Mg	Al	Si	P	S
Cl	K	Ca	Cr	Ti	Mn	Fe
Co/Ni	Cu	Zn	Y	In	As	Se
Br	Rb	Sr	Ce/La	Zr	Di/Mo	Ro/Ru

Here, we can see that the similarity ceases to exist after calcium since many elements between Ca and Cr that have now been discovered (Scandium, Vanadium) are absent. Thus, the accuracy of the table collapses after that.
This law was not accepted due to many flaws that alluded to the existence of new, undiscovered elements. The working of the d-orbital and hence the d-block elements was also not known, this contributed to the inaccuracies in Newlands’ Law of Octaves.
Additional Information:
Mendeleev published his periodic table just 4 years after Newlands’ Law, this caused Newlands’ method of classification to gain some recognition as Mendeleev’s table also showed periodicity and similarity in the elements.

Note: Please do not get confused due the word ‘octaves’. The similarity in the physical and chemical properties is seen after every seven elements in the eight element and not after every eight elements.