Calculate the formal charge on C-atom in carbonate ion.

Options

A. `+1`
B. `-1`
C. `+4`
D. zero

Answer

To calculate the formal charge on the carbon atom in the carbonate ion (CO₃²⁻), we will follow these steps:

### Step 1: Identify the Valence Electrons
First, we need to determine the number of valence electrons for the carbon atom. Carbon is in group 14 of the periodic table, which means it has 4 valence electrons.

**Hint:** Remember that the number of valence electrons corresponds to the group number for main group elements.

### Step 2: Determine the Structure of Carbonate Ion
The carbonate ion (CO₃²⁻) consists of one carbon atom and three oxygen atoms. The ion carries a -2 charge, which means there are two extra electrons in the structure.

**Hint:** Draw the Lewis structure of the carbonate ion to visualize the arrangement of atoms and electrons.

### Step 3: Count the Number of Bonds
In the carbonate ion, the carbon atom forms double bonds with one oxygen atom and single bonds with the other two oxygen atoms. This results in a total of 4 bonds (1 double bond counts as 2 bonds and 2 single bonds count as 2 bonds).

**Hint:** Count the total number of bonds formed by the carbon atom with the surrounding atoms.

### Step 4: Calculate the Number of Bonding Electrons
Each bond consists of 2 electrons. Since there are 4 bonds, the total number of bonding electrons is 4 bonds × 2 electrons/bond = 8 bonding electrons.

**Hint:** Remember to multiply the number of bonds by 2 to find the total number of bonding electrons.

### Step 5: Count the Number of Unshared Electrons
In the carbonate ion, the carbon atom does not have any unshared (lone pair) electrons. Therefore, the number of unshared electrons is 0.

**Hint:** Check the Lewis structure to see if there are any lone pairs on the carbon atom.

### Step 6: Apply the Formal Charge Formula
The formal charge (FC) can be calculated using the formula:
\[ \text{Formal Charge} = \text{Valence Electrons} - \left( \frac{\text{Bonding Electrons}}{2} + \text{Unshared Electrons} \right) \]

Substituting the values:
- Valence Electrons = 4
- Bonding Electrons = 8
- Unshared Electrons = 0

So,
\[ \text{Formal Charge} = 4 - \left( \frac{8}{2} + 0 \right) \]
\[ \text{Formal Charge} = 4 - (4 + 0) \]
\[ \text{Formal Charge} = 4 - 4 = 0 \]

### Final Result
The formal charge on the carbon atom in the carbonate ion is 0.

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