Structure of dichromate ion is:

Options

A. Linear unsymmetrical Cr-O-Cr
B. Linear symmetrical Cr-O-Cr
C. Non-Linear unsymmetrical Cr-O-Cr
D. Non-Linear symmetrical Cr-O-Cr

Answer

To determine the structure of the dichromate ion (Cr2O7^2-), we can follow these steps:

### Step 1: Identify the formula of the dichromate ion
The dichromate ion is represented as Cr2O7^2-. This indicates that there are two chromium (Cr) atoms and seven oxygen (O) atoms in the ion.

**Hint:** Remember that the charge of the ion (2-) indicates that there are two extra electrons in the structure.

### Step 2: Draw the basic structure
Start by placing the two chromium atoms in the center. The seven oxygen atoms will be arranged around them. One of the oxygen atoms will be placed between the two chromium atoms.

**Hint:** Visualize the arrangement of atoms as a central structure with surrounding atoms, similar to a star with a center and points.

### Step 3: Determine the bonding
Each chromium atom will form bonds with the surrounding oxygen atoms. In the dichromate ion, there are four double bonds and three single bonds to oxygen.

**Hint:** Remember that double bonds involve sharing two pairs of electrons, while single bonds involve sharing one pair.

### Step 4: Assign formal charges
To ensure the overall charge of the ion is -2, assign formal charges to each atom. The two chromium atoms will typically have a +6 oxidation state, and the oxygen atoms will have a -2 oxidation state, leading to the overall charge of -2.

**Hint:** Use the formula for formal charge: Formal Charge = Valence electrons - (Non-bonding electrons + 0.5 * Bonding electrons).

### Step 5: Determine hybridization
To find the hybridization of the central atoms, count the number of sigma bonds and lone pairs. The hybridization can be determined using the steric number (number of sigma bonds + lone pairs).

- For each Cr atom, there are 4 sigma bonds and 0 lone pairs, leading to sp^3 hybridization.

**Hint:** The steric number helps determine the geometry of the molecule.

### Step 6: Identify the geometry
With sp^3 hybridization, the geometry around each chromium atom is tetrahedral. However, since there are double bonds, the overall shape of the dichromate ion is non-linear.

**Hint:** Tetrahedral geometry typically suggests a 109.5° bond angle, but the presence of double bonds can alter the angles.

### Step 7: Determine symmetry
The structure of the dichromate ion is symmetrical due to the arrangement of the oxygen atoms around the chromium atoms.

**Hint:** Symmetry can often be assessed by visualizing the molecule and checking if it looks the same from different angles.

### Conclusion
The structure of the dichromate ion (Cr2O7^2-) is non-linear and symmetrical.

**Final Answer:** The correct option is D: Non-linear and symmetrical.

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