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Questions
With an example, explain Dobereiner's Triads.
State Dobereiner’s Triads giving one example.
Solution 1
- Lithium, Sodium, Potassium.
- Calcium, Strontium, Barium.
- Chlorine, Bromine, Iodine.
Solution 2
According to Dobereiner's Triads, when three elements in a triad are listed in the increasing order of their atomic masses, the atomic mass of the middle element will roughly be the average of the atomic masses of the other two elements.
For e.g.:
| Element | Atomic mass |
| Calcium | 40 |
| Strontium | 88 |
| Barium | 137 |
Average mass of calcium and barium = `(40+137)/2 = 88.5`
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| 1. | Triads | Newlands |
| 2. | Alkali metal | Calcium |
| 3. | Law of octaves | Henry Moseley |
| 4. | Alkaline earth metal | Sodium |
| 5. | Modern Periodic Law | Dobereiner |
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- Be, Mg, Ca
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40 Explain by giving reason.
