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PERIODIC TABLE DEVELOPED BY Newland .explain with points its limitations ,drawbacks and acheivements. {chap periodic classification of elements ]

Newlands Law of Octaves

After Dobereiner triad, John Newland purposed another way of classification in 1864.

"According to the law of octave, when elements are placed in increasing order of their atomic mass, every eighth element shows similarity with the preceding eighth element in their physical and chemical properties."

Newland's law of octaves was also based on musical notes. He arranged all the known elements in increasing order of their atomic mass. He found that in this arrangement, the first and eighth elements are similar in their chemical and physical properties. Hence there is a periodicity in elements when they are arranged in increasing order of their atomic masses.

For example, if we start from Lithium (atomic mass = 6) and arrange elements in increasing order of their atomic masses, the eighth element will be sodium (atomic mass = 23). Both elements show the same physical and chemical properties. Today, we known that both are alkali metals, located in group-1, and hence show same properties.

   Newlands Periodic Table

Newland arranged all the known elements in the form of a table. There are some vertical rows, later termed as periods, and vertical columns which were later termed as groups. Newland's periodic table is shown below:

In the second column, Beryllium (Be) is the first element and Magnesium (Mg) is the eighth one. After magnesium the next eighth elements is calcium (Ca). Hence according to Newland's law, these elements should show similar chemical and physical properties.

In another vertical column with carbon (C) as the first element, the eighth element is silicon (Si). Both C and Si also show similar properties. Both are non-metals and show tetravalency. Thus Newland's law of octaves holds good for all these given columns. Similarly, the last group of halogens, from fluorine (F) to chlorine (Cl) also show similarity in their properties.

Limitations of Newlands Law of Octaves

1. This classification was good with a few elements only, and was not applicable to all elements. It was not valid for elements having atomic masses higher than Ca.

2. After the discovery of Nobel gases, it became difficult to fit them in Newland’s periodic table.

3. Newland’s octave law gave a very important term of periodicity which was repeated in further classifications.

4. His classification was based on the concept that the atomic mass of an element is the periodic function of it's chemical and physical properties.

5. The same concept of periodicity of elements was repeated in Moseley’s classification and the latest long form of periodic table is also based on the same concept. The only change is the use of atomic number instead of atomic mass.

6. Newland’s octave law was good till 1913. But in 1913 Henry Moseley established a new concept that the properties of elements varied periodically according to atomic number, not atomic weight.