The sum of the total number of sigma bonds between chromium and oxygen atoms in chromate and dichromate ions is

Answer

To find the sum of the total number of sigma bonds between chromium and oxygen atoms in chromate and dichromate ions, we will analyze the structures of both ions step by step.

### Step 1: Analyze the Chromate Ion (CrO4²⁻)
1. The chromate ion has the formula CrO4²⁻.
2. In the chromate ion, chromium (Cr) is bonded to four oxygen (O) atoms.
3. The structure of the chromate ion can be represented as follows:
- Cr is at the center with four O atoms surrounding it.
- Two of the O atoms are double bonded to Cr, and the other two are single bonded.
4. Each double bond consists of one sigma bond and one pi bond, while each single bond consists of one sigma bond.
5. Therefore, the total number of sigma bonds in the chromate ion is:
- 2 (from the double bonds) + 2 (from the single bonds) = 4 sigma bonds.

### Step 2: Analyze the Dichromate Ion (Cr2O7²⁻)
1. The dichromate ion has the formula Cr2O7²⁻.
2. In the dichromate ion, there are two chromium (Cr) atoms and seven oxygen (O) atoms.
3. The structure of the dichromate ion can be represented as follows:
- Each Cr is bonded to a combination of double and single bonded O atoms.
4. In the dichromate ion, there are:
- 4 O atoms double bonded to Cr (2 sigma bonds from each double bond) = 4 sigma bonds.
- 3 O atoms single bonded to Cr = 3 sigma bonds.
5. Therefore, the total number of sigma bonds in the dichromate ion is:
- 4 (from the double bonds) + 4 (from the single bonds) = 8 sigma bonds.

### Step 3: Calculate the Total Sigma Bonds
1. Now, we will sum the total number of sigma bonds from both ions:
- Sigma bonds in chromate = 4
- Sigma bonds in dichromate = 8
2. Total sigma bonds = 4 + 8 = 12.

### Final Answer
The sum of the total number of sigma bonds between chromium and oxygen atoms in chromate and dichromate ions is **12**.

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