Explain Dobereiner’s triads.
Explain Dobereiner’s triads.
Dobereiner’s triads were the group of elements having similar properties that were identified by German scientist Johann Wolfgang döbereiner.
Döbereiner noted that the groups of three elements called triads could be formed in which all the elements have similar physical and chemical properties.
He had given the law of triads that the average of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad.
For example:
Triad 1 was made up of the alkali metals that are lithium, sodium, and potassium.
Elements Atomic Masses Lithium 6.94 Sodium 22.99 Potassium 39.1
Here you can see the average mass of potassium and lithium is equal to 23.02, which is almost equal to the atomic mass of sodium which is 22.99.
In Triad 2, as mentioned earlier, calcium, barium and strontium formed another one of Dobereiner’s triads.
Elements 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.
Elements Atomic Masses Chlorine 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.
Elements 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.
Elements 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.
Dobereiner’s triads were the group of elements having similar properties that were identified by German scientist Johann Wolfgang döbereiner.
Döbereiner noted that the groups of three elements called triads could be formed in which all the elements have similar physical and chemical properties.
He had given the law of triads that the average of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad.
For example:
Triad 1 was made up of the alkali metals that are lithium, sodium, and potassium.
| Elements | Atomic Masses |
| Lithium | 6.94 |
| Sodium | 22.99 |
| Potassium | 39.1 |
Here you can see the average mass of potassium and lithium is equal to 23.02, which is almost equal to the atomic mass of sodium which is 22.99.
In Triad 2, as mentioned earlier, calcium, barium and strontium formed another one of Dobereiner’s triads.
| Elements | 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.
| Elements | Atomic Masses |
| Chlorine | 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.
| Elements | 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.
| Elements | 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.
