How many Cr-O bonds are equivalent in chromate dianion ?

Explanation

To determine how many Cr-O bonds are equivalent in the chromate dianion (Cr2O7^2-), we can follow these steps:

### Step 1: Identify the structure of chromate dianion
The chromate dianion is represented as Cr2O7^2-. It consists of two chromium (Cr) atoms and seven oxygen (O) atoms.

### Step 2: Draw the Lewis structure
In the Lewis structure of the chromate ion, we can see that there are two chromium atoms that are each bonded to four oxygen atoms. The structure can be depicted as:

```
O
||
Cr=O
|
O^-
|
Cr=O
||
O
```

### Step 3: Identify the types of bonds
In the chromate ion, there are both double bonds (Cr=O) and single bonds (Cr-O^-). Each chromium atom is bonded to two oxygen atoms via double bonds and two oxygen atoms via single bonds.

### Step 4: Determine the equivalent bonds
In the chromate ion, the Cr-O single bonds are equivalent to each other, and the Cr=O double bonds are also equivalent to each other.

### Step 5: Count the equivalent bonds
- There are 4 Cr-O single bonds (2 from each Cr atom).
- Each of these single bonds is equivalent due to resonance.
- There are also 2 Cr=O double bonds, which are also equivalent due to resonance.

### Conclusion
In total, there are 6 equivalent Cr-O bonds in the chromate dianion (4 single bonds and 2 double bonds).

### Final Answer
Thus, the number of equivalent Cr-O bonds in the chromate dianion is **6**.

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