According to the Law of Octaves, while arranging the elements in increasing order of their atomic masses in the periodic table, the eighth element’s properties are similar to that of the first. The elements in the Newlands Law were divided into horizontal rows and each row was comprised of 7 elements. Thus, each element in the parallel row must have similar physical and chemical properties. But this is not true. The periodicity is only valid till calcium.
An example of the Law of Octaves is lithium, sodium, and potassium; they share the same physical and chemical properties. The remaining elements after potassium (Cu, Rb, Ag, and more) are different. Those elements do not show similarities to the former elements. This is the reason why the law of octaves fails to incorporate transition metals.
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Examples:
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The eighth element of lithium is sodium. Similarly, the eight-element from sodium is potassium, and all three have similar chemical properties.
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The eighth element from fluorine is chlorine. Fluorine and chlorine have similar chemical properties.
History of the Law of Octaves
In chemistry, the law of octaves was proposed by the English chemist J.A.R. Newlands in 1865. Newlands was one of the first to notice a periodic pattern in the elements’ properties and predicted later developments of the periodic law. He observed that when elements were arranged to increase atomic masses, there was much similarity in the properties of every eighth element like the musical notes do, re, me, etc. Newland named this repetition as the law of octaves.
Advantages of Newland’s Law of Octaves
Advantages of Newland’s law of octaves are listed below:
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This law gives a basis for the classification of an element having similar properties into groups of elements.
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The law provided a broad scope to order all known elements into a tabular form.
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Newland’s law of octaves was the first to be logically based on the atomic weight, i.e., it links the elements’ properties to their atomic masses.
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This system worked quite better for the lighter elements. For example, lithium, sodium, and potassium.
Drawbacks of Newland’s Law of Octaves
The drawbacks of Newland’s law of octaves are as follows:
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Out of the total 56 known elements, Newland could arrange elements only up to calcium.
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Every eighth element did not show properties similar to that of the first after calcium.
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Just 56 elements were known at the time of Newlands, but afterwards, various elements were discovered.
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To adjust the existing element ordering, Newlands placed two elements in the same position, which differed in their chemical and physical properties.
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For example, iron is an element that resembles cobalt and nickel in its properties. Iron, however, is placed far away from these elements.
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The periodic table did not include noble gases because they were not discovered then.
Mendeleev’s Periodic Law
Mendeleev’s periodic law states that the properties of elements are a periodic function of their atomic mass. This means that when the elements are arranged in increasing order of their atomic mass, the physical properties and the chemical properties of the elements of the periodic table will repeat themselves in a periodic manner.
The elements were arranged in the increasing order of their atomic mass and the entire table was referred to as the periodic table. The elements that seemed to possess similar properties were grouped together in the vertical rows called columns. It contains seven horizontal rows and eight vertical columns, and the horizontal rows were known as periods.
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Solved Examples
1. Which elements were left by Mendeleev in his periodic table have been discovered later? Mention any three.
Ans. The elements discovered later that were left by Mendeleev in his periodic table are Germanium, Scandium, and Gallium.
2. Why are the noble gases placed in a separate group?
Ans. Out of all the known elements, noble gases such as Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), and Xenon (Xe) are the most inert (non-reactive) and are present in very low concentrations in our atmosphere. Therefore, they are assembled together in a separate group called zero groups in Mendeleev’s periodic table.
Hence Newland’s Law of Octaves and Mendeleev’s Periodic Law is explained in detail in the above article. History of the Law octaves, Advantages, drawbacks along with solved examples is also given.