Which will provide strong back bonding

Options

A. `BCl_3`
B. `BF_3`
C. `BBr_3`
D. `BI_3`

Answer

To determine which compound provides strong back bonding among the options BCl3, BF3, BBr3, and BI3, we need to analyze the extent of back bonding based on the overlap of orbitals between boron (the central atom) and the halogens (the surrounding atoms).

### Step-by-Step Solution:

1. **Identify the Central Atom and its Configuration**:
- The central atom in all the compounds is boron (B).
- Boron has an atomic number of 5, with an electronic configuration of 1s² 2s² 2p¹. This means it has an empty 2p orbital available for bonding.

2. **Identify the Halogens and Their Electron Configuration**:
- The halogens in the options are fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).
- Their configurations are as follows:
- Fluorine: 1s² 2s² 2p⁵ (2p orbital)
- Chlorine: 1s² 2s² 2p⁶ 3s² 3p⁵ (3p orbital)
- Bromine: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁵ (4p orbital)
- Iodine: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ 5s² 5p⁵ (5p orbital)

3. **Understanding Back Bonding**:
- Back bonding occurs when a filled orbital of a ligand (in this case, the halogen) overlaps with an empty orbital of the central atom (boron).
- The strength of back bonding is influenced by the extent of orbital overlap. Greater overlap leads to stronger back bonding.

4. **Comparing Orbital Overlaps**:
- The overlap of orbitals is strongest when both atoms involved have similar sizes and energy levels.
- In this case:
- BF3: Boron (2p) and Fluorine (2p) - strong overlap
- BCl3: Boron (2p) and Chlorine (3p) - moderate overlap
- BBr3: Boron (2p) and Bromine (4p) - weaker overlap
- BI3: Boron (2p) and Iodine (5p) - weakest overlap

5. **Conclusion**:
- The order of back bonding strength based on the extent of orbital overlap is:
- BF3 > BCl3 > BBr3 > BI3
- Therefore, the compound that provides the strongest back bonding is **BF3**.

### Final Answer:
The compound that provides strong back bonding is **BF3**.