Structure of `-BH_2` group is

Options

A. linear
B. planar
C. tetrahedral
D. octahedral

Answer

To determine the structure of the `-BH2` group, we can follow these steps:

### Step 1: Identify the Composition of the `-BH2` Group
The `-BH2` group consists of one boron (B) atom and two hydrogen (H) atoms.

### Step 2: Count the Bond Pairs and Lone Pairs
In the `-BH2` group, boron typically forms three bonds (one with each hydrogen atom and one with a potential third group or atom). However, in this case, we only have two hydrogen atoms attached to boron. Thus, we have:
- Bond pairs: 2 (from the two B-H bonds)
- Lone pairs: 0 (boron does not have any lone pairs in this case)

### Step 3: Determine the Hybridization
The hybridization can be determined based on the number of bond pairs and lone pairs. Since we have 2 bond pairs and 0 lone pairs, we use the formula:
- Hybridization = number of bond pairs + number of lone pairs = 2 + 0 = 2
This corresponds to sp² hybridization.

### Step 4: Predict the Molecular Geometry
For sp² hybridization, the molecular geometry is trigonal planar. This means that the atoms are arranged in a flat, triangular shape around the central boron atom.

### Step 5: Consider the Charge
If we consider the `-BH2` group as `BH2^-`, we need to account for an additional electron due to the negative charge. This does not change the hybridization or the geometry, as we still have 2 bond pairs and 0 lone pairs.

### Conclusion
The structure of the `-BH2` group is **trigonal planar**.

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