The list of elements given below makes three triads and names the family of each triad.
Chlorine, Lithium, Calcium, Bromine, Sodium Strontium Iodine, Potassium, and Barium.
The list of elements given below makes three triads and names the family of each triad.
Chlorine, Lithium, Calcium, Bromine, Sodium Strontium Iodine, Potassium, and Barium.
Dobereiner’s triads:
- Dobereiner told that groups of three elements (triads) could be formed in which all the elements shared similar physical and chemical properties.
- Dobereiner stated that the arithmetic mean or 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.
Triad 1 (Alkaline-earth-forming elements):
The Alkaline Earth metals Calcium, Barium, and Strontium formed one of Dobereiner’s triads:
Triad Atomic Masses in amu Calcium 40.1 Strontium 87.6 Barium 137.3
The atomic mass of Strontium equals an average of the atomic masses of calcium and barium.
Therefore the atomic mass of Strontium = which is near .
Triad 2 (Alkali-forming elements):
The alkali metals Lithium, Sodium, and Potassium formed one of Dobereiner’s triads:
Triad Atomic Masses in amu Lithium 7 Sodium 23 Potassium 39
The atomic mass of Sodium equals an average of the atomic masses of Lithium and Potassium.
Therefore the atomic mass of Sodium
Triad 3 (Salt-forming elements):
The halogens Chlorine, Bromine, and Iodine formed one of Dobereiner’s triads:
Triad Atomic Masses in amu Chlorine 35.5 Bromine 81.1 Iodine 126.9
The atomic mass of Bromine equals an average of the atomic masses of Chlorine and Iodine.
Therefore the atomic mass of Bromine =
Dobereiner’s triads:
- Dobereiner told that groups of three elements (triads) could be formed in which all the elements shared similar physical and chemical properties.
- Dobereiner stated that the arithmetic mean or 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.
Triad 1 (Alkaline-earth-forming elements):
The Alkaline Earth metals Calcium, Barium, and Strontium formed one of Dobereiner’s triads:
| Triad | Atomic Masses in amu |
| Calcium | 40.1 |
| Strontium | 87.6 |
| Barium | 137.3 |
The atomic mass of Strontium equals an average of the atomic masses of calcium and barium.
Therefore the atomic mass of Strontium = which is near .
Triad 2 (Alkali-forming elements):
The alkali metals Lithium, Sodium, and Potassium formed one of Dobereiner’s triads:
| Triad | Atomic Masses in amu |
| Lithium | 7 |
| Sodium | 23 |
| Potassium | 39 |
The atomic mass of Sodium equals an average of the atomic masses of Lithium and Potassium.
Therefore the atomic mass of Sodium
Triad 3 (Salt-forming elements):
The halogens Chlorine, Bromine, and Iodine formed one of Dobereiner’s triads:
| Triad | Atomic Masses in amu |
| Chlorine | 35.5 |
| Bromine | 81.1 |
| Iodine | 126.9 |
The atomic mass of Bromine equals an average of the atomic masses of Chlorine and Iodine.
Therefore the atomic mass of Bromine =
