(Cu, Ag, Au) does not follow Dobereiner's law of triads,why?

Explanation

To understand why the elements Copper (Cu), Silver (Ag), and Gold (Au) do not follow Dobereiner's law of triads, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Dobereiner's Law of Triads**:
- Dobereiner's law states that when three elements are grouped together (a triad), the atomic mass of the middle element should be approximately equal to the average of the atomic masses of the other two elements.

2. **Identifying the Elements**:
- The elements in question are Copper (Cu), Silver (Ag), and Gold (Au).

3. **Finding Atomic Masses**:
- The atomic masses of the elements are approximately:
- Copper (Cu) = 63.55 u
- Silver (Ag) = 107.87 u
- Gold (Au) = 196.97 u

4. **Calculating the Average Atomic Mass**:
- To check if Ag follows the law, we calculate the average of Cu and Au:
\[ \text{Average Atomic Mass} = \frac{\text{Atomic Mass of Cu} + \text{Atomic Mass of Au}}{2} \]
\[ = \frac{63.55 + 196.97}{2} = \frac{260.52}{2} = 130.26 \, \text{u} \]

5. **Comparing with Silver's Atomic Mass**:
- Now, we compare the average atomic mass calculated (130.26 u) with the atomic mass of Silver (Ag), which is 107.87 u.

6. **Conclusion**:
- Since the atomic mass of Silver (107.87 u) is not equal to the average atomic mass (130.26 u) of Copper and Gold, the triad of Cu, Ag, and Au does not satisfy Dobereiner's law of triads.

### Final Answer:
Thus, Copper (Cu), Silver (Ag), and Gold (Au) do not follow Dobereiner's law of triads because the atomic mass of Silver is not equal to the average of the atomic masses of Copper and Gold.

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