Question

Explain and calculate the

Dobereiner's third and fourth triads.​

Answer 1

Explanation:

The elements selenium, tellurium, and sulfur made up the fourth triad. The arithmetic mean of the masses of both the first and third elements in this triad corresponds to the value of 79.85. Cobalt, nickel, and Iron constituted the last of the Dobereiner's triads.

In the history of the periodic table, Döbereiner's triads were an early attempt to sort the elements into some logical order by their physical properties. In 1817, a letter reported Johann Wolfgang Döbereiner's observations of the alkaline earths; namely, that strontium had properties that were intermediate to those of calcium and barium.[1] By 1829, Döbereiner had found other groups of three elements (hence "triads") whose physical properties were similarly related.[2] He also noted that some quantifiable properties of elements (e.g. atomic weight and density) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements.

Answer 2

Answer:

Here's your answer

Explanation:

Dobereiner's law of triads: When elements are arranged in order of increasing atomic masses,groups of three elements(triads), having similar chemical properties are obtained. The atomic mass of the middle elements of the triad being equal to the arithmetic mean of the atomic masses of the other two elements.

For example: Alkali metal group ( Dobereiner's triad) : Lithium is the 1st element, sodium is the middle element whereas potassium is the 3 rd element of the triad.

Triad 1

This triad was made up of the alkali metals lithium, sodium, and potassium.

Triad Atomic Masses

Lithium = 6.94

Sodium = 22.99

Potassium = 39.1

The arithmetic mean of the masses of potassium and lithium corresponds to 23.02, which is almost equal to the atomic mass of sodium.

Triad 2

As mentioned earlier, calcium, barium, and strontium formed another one of Dobereiner’s triads.

Triad Atomic Masses

Calcium = 40.1

Strontium = 87.6

Barium = 137.3

The mean of the masses of barium and calcium corresponds to 88.7.

Triad 3

The halogens chlorine, bromine, and iodine constituted one of the triads.

Triad Atomic Masses

hlorine = 35.4

Bromine = 79.9

Iodine = 126.9

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

Triad 4

The fourth triad was formed by the elements sulfur, selenium, and tellurium.

Triad Atomic Masses

Sulfur = 32.1

Selenium = 78.9

Tellurium = 127.6

The arithmetic mean of the masses of the first and third elements in this triad corresponds to 79.85.

Triad 5

Iron, cobalt, and nickel constituted the last of Dobereiner’s triads.

Triad Atomic Masses

Iron = 55.8

Cobalt = 58.9

Nickel = 58.7

However, the mean of the atomic masses of iron and nickel corresponds to 57.3.

Hope your understand.