Newlands Law Of Octaves, Dobereiner Triads, and Law of Triads with Example

 

Newlands� Law of Octaves: The attempts of D�bereiner encouraged other chemists to correlate the properties of elements with their atomic masses. In 1866, John Newlands, an English scientist, arranged the then-known elements in the order of increasing atomic masses.

 

He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element. He found that every eighth element had properties similar to that of the first. He compared this to the octaves found in music. Therefore, he called it the �Law of Octaves�.

 

It is known as �Newlands� Law of Octaves�. In Newlands� Octaves, the properties of lithium and sodium were found to be the same. Sodium is the eighth element after lithium. Similarly, beryllium and magnesium resemble each other. A part of the original form of Newlands� Octaves is shown here.

 

Explain the limitations of Newland's law of octaves

 

The following were the major drawbacks of Newlands' law of octaves:

 

• It only applied to lighter elements with atomic weights of up to 40 u, i.e. up to calcium. After calcium, the first and eighth elements had no qualities in common. Chromium (Cr) and yttrium (Y), for example, are the first and eighth elements in the same column, although they have completely distinct characteristics.
• Only 63 elements were thought to exist in nature, with no new elements expected to be discovered in the future. However, several additional elements were discovered subsequently that have properties that contradicted the law of octaves.
• Some elements that are similar have been separated from one another, while others that are dissimilar have been grouped together in the same column. Iron (Fe), for example, is similar to cobalt (Co) and nickel (Ni), although it has been placed far from these elements. Similarly, cobalt and nickel aren't halogens (F, CI, Br), but they're grouped together in the same column.
• When noble gases were found, the eighth element's properties were no longer comparable to those of the first. Actually, the first and ninth elements have properties that are similar.
• In order to fit elements into his Table, Newlands adjusted two elements in the same slot, but also put some unlike elements under the same note.

 

Thus, Newlands� Law of Octaves worked well with lighter elements only.

Dobereiner Triads

In the year 1817, Johann Wolfgang D�bereiner, a German chemist, tried to arrange the elements with similar properties into groups. He identified some groups having three elements each. So he called these groups �triads�.

 

D�bereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

For example, take the triad consisting of lithium (Li), sodium (Na), and potassium (K) with the respective atomic masses 6.9, 23.0, and 39.0.

 

One of the limitations of this classification was that D�bereiner could identify only three triads from the elements known at that time. Hence, this system of classification into triads was not found to be useful.

Read More: Periodic Classification Of Elements - Trends in Modern Periodic Table

 

Law Of Octaves - FAQs