According to C.F.T, attraction between the central metal ion and ligands in a complex is purely electrostatic. The transition metal which forms the central atom cation in the complex is regarded as a positive ion. It is surrounded by negative ligands or neutral molecules which have a lone apir of electrons, if the ligand is a neutral molecule such as `NH_(3)`, the negative and of the dipole in the molecule is directed towards the metal cation. the electrons on the central metal ion are under repulsive forces from those on the ligands. thus the electrons occupy the d-orbitals remain away from the direction of approach ligands. ltBrgt Q. The crystal field-spliting order for `Cr^(3+)` cation is octahedral field for ligands `CH_(3)COO^(-),NH_(3),H_(2)O,CN^(-)` is:

Options

A. `CH_(3)COO^(-) lt H_(2)O lt NH_(3) lt CN^(-)`
B. `CH_(3)COO^(-) lt NH_(3) lt H_(2)O lt CN^(-)`
C. `H_(2)O lt CH_(3)COO^(-) lt NH_(3) lt CN^(-)`
D. `NH_(3) lt CH_(3)COO^(-) lt H_(2)O lt CN^(-)`

Answer

To determine the crystal field splitting order for the `Cr^(3+)` cation in an octahedral field with the ligands `CH3COO^(-)`, `NH3`, `H2O`, and `CN^(-)`, we follow these steps:

### Step 1: Identify the oxidation state and electronic configuration of `Cr^(3+)`
- Chromium (Cr) has an atomic number of 24. In the +3 oxidation state, it loses three electrons.
- The electronic configuration of neutral chromium is `[Ar] 3d^5 4s^1`. For `Cr^(3+)`, it becomes `[Ar] 3d^3`.

**Hint:** Remember that the oxidation state affects the number of d-electrons available for splitting.

### Step 2: Understand the nature of the ligands
- The ligands provided are:
- `CH3COO^(-)` (acetate) - weak field ligand
- `NH3` (ammonia) - moderate field ligand
- `H2O` (water) - weak field ligand
- `CN^(-)` (cyanide) - strong field ligand

**Hint:** Classify ligands based on their strength using the spectrochemical series.

### Step 3: Rank the ligands based on their field strength
- According to the spectrochemical series, the order of field strength from strongest to weakest for the given ligands is:
1. `CN^(-)` (strongest)
2. `NH3`
3. `H2O`
4. `CH3COO^(-)` (weakest)

**Hint:** Use the spectrochemical series to determine the relative strengths of the ligands.

### Step 4: Determine the crystal field splitting order
- In an octahedral field, the d-orbitals split into two sets: `t2g` (lower energy) and `eg` (higher energy).
- Strong field ligands cause a larger splitting of the d-orbitals, while weak field ligands cause smaller splitting.

**Hint:** Remember that the stronger the ligand, the greater the splitting of the d-orbitals.

### Step 5: Write the final crystal field splitting order
- Based on the ligand strength, the crystal field splitting order for `Cr^(3+)` in the presence of the given ligands is:
- `CN^(-) > NH3 > H2O > CH3COO^(-)`

**Final Answer:** The crystal field splitting order for `Cr^(3+)` cation in octahedral field is:
- `CN^(-) > NH3 > H2O > CH3COO^(-)`