Dobereiner’s Triads and Law of Octaves

According to Dobereiner’s laws of triads, when some elements of chemical groups form in order to increase atomic masses, triads or groups of three elements have similar chemical properties to obtain. The atomic mass of the middle element of the triads can be equal to the arithmetic mean of the atomic masses of the other two elements.

For example, the alkali metal group is a triad, where lithium is the 1st element, sodium is the middle one, and potassium is the 3rd or last one.  

Dobereiner’s Law of Triads

The Dobereiner’s triads first originated in the year 1817. On the other hand, several new alkaline earth metals, including barium, calcium, and strontium, were also identified. However, in the year 1829, three more triads were also organized. 

Dobereiner’s triads represent the group of elements that exhibit properties similar to each other. These elements are further identified by the German Chemist named Johann Wolfgang Dobereier. That is the reason the Law is also named after him. He stated that the groups of three triads can take place in a way where all the elements share the same chemical and physical properties. 

Dobereiner further concluded in his Dobereiner’s triads that the arithmetic means of the atomic masses of the first and the third element present in the triad would be somewhat similar to the atomic masses of the second element present in the same triad.

Furthermore, he also confirmed that this Law can identify the quantifiable properties of the elements. This can also include the density.

The limitations present in Dobereiner’s triads are:

• The elements which are newly discovered do not fit into triads.
• There are only 5 identified Dobereiner’s triads available
• The model became obsolete after the identification of new elements
• Several known elements also do not fit in the triads

Newlands Law of Octave

In the year 1864, a British Chemist named John Newlands went to identify the 62 elements that were known at that time in the periodic table. Also, to obtain all the information of the same, he organized the whole table in ascending order, further relying on the atomic masses. Also, this further stated that the 8th elements include the same amount of properties. Based on this observation, he deciphered the Law Octave.  

Thus, with the help of this Law, it was further found that every 8th property present in the table would have the same properties only when these are assigned in increasing order on the basis of the atomic masses. 

Also, Newland differentiates the commonness of the elements with the help of Dobereiner’s triads. And these are the first and the foremost attempt required for the assigning of the elements.

Limitations of Newlands Law of Octave

The limitations of Newlands Law of Octaves are further listed:

• Several dissimilar octaves are grouped together, like halogens. They are grouped with metals like nickel, platinum, cobalt.
• Elements up to calcium are only proved true in the Law. Greater atomic masses related elements are not supported by this Law.
• In the periodic classification, several elements are placed in the same slots.
• Newly discovered elements are not suitable and fit for the Law or octave pattern.

Attempts to Organize the Elements:

Within 1700, a handful of elements were isolated and identified, including lead and copper. Also, with the development of technologies, several new elements are found, and for this reason, several scientists organized several ways to find these new elements. Such elements are like Nihonium, Moscovium, Tennessine, etc. 

However, the logical manner of groping the elements according to the Law of triads can be further identified with the help of Dobereiner’s triad’s examples. These are further tabulated under for your better understanding:

Triad 1: Triad 1 was formed with the alkali metals sodium, potassium, and lithium. However, these are organized according to the atomic masses. The Dobereiner’s triad’s examples:

• Lithium- 6.94
• Sodium- 22.99
• Potassium- 39.1

Thus the atomic masses give the arithmetic means that corresponds to 23.02 and are also similar to the atomic mass of sodium. 

Triad 2: Calcium, strontium, and barium are some strong examples of the Law of triads. 

• Barium- 137.3,
• Calcium- 40.1
• Strontium- 87.6

Thus the mean of the masses of these three triad forms 88.7. 

Triad 3: The halogens, iodine, chlorine, and bromine are a part of the third triad:

• Bromine- 79.9
• Chlorine- 35.4
• Iodine- 126.9

The mean value of the atomic masses of iodine and chlorine is 81.1. 

Triad 4: The fourth triad was constructed with the help of the elements sulfur, tellurium, and selenium. 

• Sulfur- 32.1
• Tellurium- 127.6
• Selenium- 78.9

The arithmetic mean of the masses of the first and the third element is represented by the corresponding value of 79.85.  

Triad 5: Cobalt, Iron, and Nickel are the fifth Dobereiner’s triad’s examples that lie in the third triad. 

• Cobalt- 58.9
• Iron- 55.8
• Nickel- 58.7

The mean of this is further considered to be almost 57.3. 

Conclusion

It can be concluded that the study of Dobereiner’s triads focuses on various limitations on the periodic table. Still, his chapter is important for understanding the details of the periodic table. Thus some brief studies regarding Dobereiner’s triads are available, along with its limitations and method of organizing the elements in the periodic element. This is the base topic for class 11 chemistry.