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Considering the large number of new elements that were found during the eighteenth and nineteenth centuries, the broad classification of elements into metals and non-metals proved ineffective. There were a number of studies carried out in order to find pieces that shared similar characteristics and group them together.
What are Dobereiner’s Triads, and how do they work?
Dobereiner’s triads were groups of elements having similar properties that were discovered by the German scientist Johann Wolfgang Dobereiner in the early nineteenth century. His observations included the discovery that groups of three elements (triads) could be produced in which all of the elements had comparable physical and chemical properties.
As stated in his law of triads, the arithmetic mean of the atomic masses of the first and third elements in a triad would be nearly equal to the atomic mass of the second element in that triad. However, Dobereiner did not indicate how he arrived at this result. He also stated that this equation may be extended to include other quantitative attributes of elements, such as density, in addition to the ones already mentioned.
When Dobereiner discovered his first triad in 1817, it was composed of the alkaline earth metals calcium, strontium, and barium. This was the first of Dobereiner’s triads to be discovered. By the year 1829, a total of three new triads had been discovered. These triads are listed in the table below.
Triad Number One
The alkali metals lithium, sodium, and potassium formed the basis of this triad of elements.
Atomic Masses in a Triad
Lithium 6.94
Sodium 22.99
Potassium 39.1
The arithmetic mean of the atomic masses of potassium and lithium is 23.02, which is nearly equivalent to the atomic mass of sodium in terms of atomic weight.
Triad number two
As previously established, the elements calcium, barium, and strontium formed another of Dobereiner’s triads of elements.
Atomic Masses in a Triad
Calcium 40.1
Strontium 87.6
Barium 137.3
Barium and calcium have masses that are on average 88.7 grams each, according to the formula.
Triad number three
Triad 3 was made up of the halogens chlorine, bromine, and iodine, which together formed one of the triads.
Atomic Masses in a Triad
Chlorine 35.4
Bromine 79.9
Iodine 126.9
The average atomic masses of chlorine and iodine are 81.1 and 81.1, respectively.
Triad number four
The elements sulphur, selenium, and tellurium comprised the fourth triad, which was the most powerful.
Atomic Masses in a Triad
Sulfur 32.1
Selenium 78.9
Tellurium 127.6
It is calculated that the arithmetic mean of the masses of the first and third elements in this triangular arrangement is 79.85.
Triad Number five
Dobereiner’s triad of iron, cobalt, and nickel was the final element in his composition.
Atomic Masses in a Triad
Iron 55.8
Cobalt 58.9
Nickel 58.7
The mean of the atomic masses of iron and nickel, on the other hand, equals 57.3.
Limitations
The following are the most significant limitations of Dobereiner’s approach of classifying elements.
Because of the discovery of additional elements, this model has become obsolete.
The newly found elements did not fit into any of the triads that had been established.
There were a total of 5 Dobereiner’s triads found in the study.
Even numerous well-known elements were unable to fit into any of the triumvirate’s categories.
As a result of these inadequacies, additional classification methods for elements have been created.
Newland’s Law of Octaves is a mathematical formula that describes how many octaves there in a given interval of time.
The British chemist John Newlands attempted to synthesise all 62 elements that were known at the time in the year 1864. He organised them in ascending order based on their atomic masses and discovered that every eighth element had qualities that were comparable to the previous element. Newland’s law of octaves was created as a result of this finding.
When the elements are organised in ascending order of their atomic masses, the law of octaves asserts that every eighth element has qualities that are comparable to the attributes of the elements before it. An illustration describing the components with comparable qualities in accordance with Newland’s law of octaves is shown in the next section.
Newland’s Law of Octaves is a mathematical formula that describes how many octaves there in a given interval of time.
Using music as an example, Newlands noted that every eighth note is equivalent to the initial note, and that the similarities between the elements are akin to octaves of music. This was the first effort at giving an atomic number to each element in the periodic table of elements. Nonetheless, this way of categorising materials was received with a great deal of opposition among the scientific community.
Conclusion
Therefore it can be concluded, Newland’s law of octaves was only valid for elements up to and including calcium. Elements having larger atomic masses were unable to be accommodated within octaves of the scale.
The elements that were discovered later on were unable to be accommodated inside the octave structure. So there was no room for new elements to be discovered as a result of using this strategy for categorising existing elements.
