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Newlands law of Octaves: Definition and limitations

The idea of Dobereiner's triads encouraged chemists to search for other trends between the properties of elements and their atomic masses. In 1866, John Alexander Newlands, an English scientist, arranged the then known elements in order of increasing atomic masses (Table below). He started with hydrogen, the element having the lowest atomic mass and ended with thorium which was the 56th element. He found that the properties of the eighth element (because noble gasses were not known at that time) were similar to the properties of the first element. He compared this with the octaves found in musical scale. Therefore, he called it as Newlands's Law of Octaves. Thus, according to Newlands's Law of Octaves,

When elements were arranged in horizontal rows in order of their increasing relative atomic masses, the properties of every eighth element were similar to the first one, like the eighth note of a musical scale .


There are seven musical notes. In the Indian system of music, these are called : sa, re, ga, ma, pa, dha, ni while in the western system of music, these are called do, re, mi, fa, so, la, ti. A musician uses only these seven notes for composing the music of a song. Obviously, there must be some repetition of notes. Every eighth note (sa) is similar to the first one (sa) and the whole music of the song is composed by repeating these seven notes over and over again.{alertInfo}


Now if we take lithium (Li) as the first element then 8th elements from it will be sodium. According to newlands law of octaves, these two elements must have similar properties. It has actually been found that lithium and sodium have similar properties.

Serial No.

1

2

3

4

5

6

7

Notes of Musical scale (western music)

do

re

mi

fa

so

la

ti

Notes of Musical scale (Indian music)

sa

re

ga

ma

pa

dha

ni

Elements with atomic mass upto 40 u

H

F

Cl

Ki

Na

K

Be

Mg

Ca

B

Al

C

Si

N

P

O

S

Elements with atomic mass> 40 u


Co & Ni

Br


Cu

Rb


Zn

Sr

Cr

Y

Ce, La

Ti

ln

Zr

Mn

As

--

Fe

Se

--


Again, if we take sodium (Na) as the first element, then the eighth element from it will be potassium (K). According to Newlands's Law of Octaves, these two elements must have similar properties. This has actually been found to be so. In fact, all the three elements, lithium, sodium and potassium have similar properties.

To illustrate the law of octaves further, let us take beryllium (Be) as the first element, then the eighth element from it will be magnesium (Mg). Then according to Newlands's Law of Octaves, these two elements should have similar properties. It has actually been found that beryllium and magnesium have similar chemical properties. Again, if we take magnesium (Mg) as the first element, then the eighth element from it will be calcium (Ca). Now, according to Newlands's Law of Octaves, these two elements should have similar properties. Actually it has been found that both magnesium and calcium have similar chemical properties. In fact, all the three elements, i.e ., beryllium, magnesium and calcium have similar chemical properties. In a similar way, we can explain that the first and the eighth element from it in each of the following pairs have similar properties. Thus, boron (B) and aluminum (Al), carbon (C) and silicon (Si), nitrogen (N) and phosphorus (P), oxygen (O) and sulphur (S) and, fluorine (F) and chlorine (CI) have similar chemical properties.


The Royal Society, London recognised the work of Newlands much later and awarded him the Davy Medal in 1887.


Limitations of Newlands law of Octaves

1. Newlands's law of octaves was applicable only to lighter elements having atomic masses upto 40 u, i.e ., upto calcium. After calcium, every eighth element did not possess properties similar to that of the first. For example, if we start with chromium (Cr) as the first element (Table above), then the eighth element from it will be yttrium (Y). These two elements have entirely different properties. Similarly from Table above, we find that first and the eighth element from it in each of the following pairs have altogether different properties. Thus, titanium (Ti) and indium (In), indium and zirconium, manganese (Mn) and arsenic (As) and, iron (Fe) and selenium (Se) have altogether different properties.


2. It was assumed by Newlands that only 56 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.


3. In order to fit elements into his Table above, Newlands not only placed two elements in the same slot but also placed some unlike elements in the same column. For example, cobalt (Co) and nickel (Ni) are placed in the same slot and these are placed in the same column as that of fluorine, chlorine and bromine which have very different properties. On the other hand, iron (Fe) which resembles cobalt and nickel in properties has been placed far away from these elements. Similarly, Ce and La have been placed at the same slot under the same column of Cr and Y though their properties are altogether different from those of Cr or Y.


4. Noble gasses were not known when Newlands gave his law of octaves. However, when noble gasses were discovered around the year 1900, 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 had similar properties.


In view of the above limitations, the Newlands's Law of Octaves was discarded.