Dobereiner’s Triads

Various attempts have been made from ancient times to classify elements into groups based on their properties. As additional elements were found, a variety of theories for classifying them arose. To justify their classification, various scientists employed varied methodologies and evidence. These theories were improved over time, culminating in the creation of the present periodic table. Let’s take a look at Dobereiner’s triads, which is one of these classic theories.

Dobereiner Triads

Johann Wolfgang Dobereiner, a German scientist, discovered that elements with similar properties may be grouped together in triads (groups of three). The chemical and physical properties of the elements in a particular trio were similar.

Law of Triads

When atoms are grouped in ascending order of their atomic masses, according to Dobereiner, the arithmetic mean of the atomic masses of the first and third elements in a trio is nearly equal to the atomic mass of the second element in that triad. He went on to say that this law applied to other qualities of elements as well. Density was one of these characteristics.

Various Dobereiner’s Triads  

In 1817, the first Dobereiner’s triad was discovered. Calcium, strontium, and barium are alkaline earth metals that make up this compound. Three more triads were identified later on. Let’s take a closer look at these triads. The following are five of Dobereiner’s triads:

Triad 1: The alkali metals lithium, sodium, and potassium made up this triad.

Lithium is an element with a high atomic mass.

7

Sodium

23

Potassium

39

For this triad, the law of triads can be confirmed as follows:

(Atomic Mass of Lithium + Atomic Mass of Potassium) / 2 Equals Sodium’s atomic mass

= (39 + 7)/2

46/2 = 23

As a result, the law of triads is proven for this triad.

Triad 2: Alkaline earth metals, such as calcium, strontium, and barium, make up this triad.

Calcium is an element with a high atomic mass.40

Strontium-87.6

Barium-137

Let’s see if the law of triads applies to this triad as well.

(40 + 137) / 2 = (Atomic Mass of Calcium + Atomic Mass of Barium)

177/2 =87.5 %

87.5 is quite near to Strontium’s atomic mass. The law of triads is thus confirmed.

Triad 3: Halogens (Chlorine, Bromine, and Iodine) make up this triad.

Element

Atomic Mass is the mass of an atom.Chlorine-35.5

Bromine-80

Iodine-127

The Law of Triads may be confirmed once more for this triad.

Bromine Atomic Mass = (Chlorine Atomic Mass + Iodine Atomic Mass) / 2

= (35.5 + 127)/2 = (35.5 + 127)/2 = (35.5 + 127)/2

162.5/2 =81.25

which is pretty near to Bromines atomic mass As a result, the law of triads is proven.

Sulfur, selenium, and tellurium made up the fourth triad.

Element

Atomic Mass is the mass of an atom.

Sulfur-32

Selenium-79

Tellurium-128

The atomic masses of Sulfur and Tellurium have an arithmetic mean of 80, which is quite near to the atomic mass of Selenium.

Triad 5: Iron, cobalt, and nickel were the elements in this triad.

Element

Atomic Mass is the mass of an atom.

Iron-55.8

Cobalt-58.9

Nickel-58.7

Cobalt has an atomic mass of 57.25, which is almost equivalent to the arithmetic mean of the atomic masses of Iron and Nickel.

Limitations of Dobereiner’s triads

Despite the fact that Dobereiner’s triads attempted to classify elements based on their attributes into groups of three, they still had a number of drawbacks, which are mentioned below:

1.Many additional elements were discovered in the 18th and 19th centuries, making Dobereiner’s triads classification problematic, if not impossible in some situations.

2.Only five Dobereiner’s triads could be found, and no additional elements could be grouped into them.

3.At the time of Dobereiner’s triads development, there were also some factors that did not fit into Dobereiner’s triads.

4.As a result, the element collection became disorganized.

5.Despite the fact that Dobereiner’s triads were unable to classify all elements according to their properties, they laid the groundwork for the contemporary periodic table.

Conclusion 

Johann Wolfgang Dobereiner, a German scientist, discovered Dobereiner’s triads, which were groups of elements having similar properties. He noticed that triads (groups of three elements) could be constructed with all of the elements having comparable physical and chemical properties.