Number of `Cr-O` sigma bonds in dichromate ion `Cr_(2)O_(7)^(2-)` is

Options

A. 6
B. 7
C. 8
D. 4

Answer

To determine the number of Cr-O sigma bonds in the dichromate ion \(\text{Cr}_2\text{O}_7^{2-}\), we can follow these steps:

### Step 1: Understand the Structure of Dichromate Ion
The dichromate ion \(\text{Cr}_2\text{O}_7^{2-}\) consists of two chromium (Cr) atoms and seven oxygen (O) atoms. The structure can be visualized as two Cr atoms connected by oxygen atoms.

### Step 2: Draw the Lewis Structure
To accurately count the sigma bonds, we need to draw the Lewis structure of the dichromate ion. In the Lewis structure, we can see that each chromium atom is bonded to several oxygen atoms.

### Step 3: Identify the Types of Bonds
In the dichromate ion, the bonds between Cr and O can be either single or double bonds. A single bond is a sigma bond, while a double bond consists of one sigma bond and one pi bond.

### Step 4: Count the Sigma Bonds
1. Each Cr atom forms:
- 2 single bonds with oxygen atoms (2 sigma bonds)
- 2 double bonds with oxygen atoms (2 sigma bonds from each double bond)

2. Therefore, for each chromium atom:
- 2 (from single bonds) + 2 (from double bonds) = 4 sigma bonds per Cr atom.

3. Since there are 2 Cr atoms:
- Total sigma bonds = \(4 \text{ (from one Cr)} \times 2 \text{ (Cr atoms)} = 8 \text{ sigma bonds}\).

### Conclusion
The total number of Cr-O sigma bonds in the dichromate ion \(\text{Cr}_2\text{O}_7^{2-}\) is **8**.

### Final Answer
The answer is **8** sigma bonds.

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