Structure of `Na_(2)[B_(4)O_(5)(OH)_(4)]*8H_(2)O` contains

Options

A. two triangular and two tetrahedral units
B. three triangular and one tetrahedral units
C. all tetrahedral units
D. all triangular units

Answer

To determine the structure of `Na2[B4O5(OH)4]·8H2O`, we can break down the components and analyze the arrangement of atoms and their hybridization. Here’s a step-by-step solution:

### Step 1: Identify the Components
The formula `Na2[B4O5(OH)4]·8H2O` consists of:
- Sodium ions (Na⁺)
- Boron atoms (B)
- Oxygen atoms (O)
- Hydroxyl groups (OH)
- Water molecules (H2O)

### Step 2: Count the Atoms
From the formula:
- There are 2 Sodium (Na) ions.
- There are 4 Boron (B) atoms.
- There are 5 Oxygen (O) atoms from the borate structure and 4 from hydroxyl groups, totaling 9 Oxygen atoms.
- There are 4 Hydroxyl (OH) groups.
- There are 8 Water (H2O) molecules.

### Step 3: Understand the Structure
The compound is known as borax, which has a specific arrangement of boron and oxygen. The structure consists of:
- 2 triangular units (formed by boron and oxygen)
- 2 tetrahedral units (formed by boron and oxygen)

### Step 4: Draw the Structure
1. **Triangular Units**: Each triangular unit consists of a boron atom surrounded by three oxygen atoms.
2. **Tetrahedral Units**: Each tetrahedral unit consists of a boron atom surrounded by four oxygen atoms.

### Step 5: Assign Hybridization
- For the triangular units (B atoms with 3 bond pairs and 0 lone pairs), the hybridization is **sp²**.
- For the tetrahedral units (B atoms with 4 bond pairs and 0 lone pairs), the hybridization is **sp³**.

### Step 6: Overall Structure
The overall structure of `Na2[B4O5(OH)4]·8H2O` can be summarized as:
- 2 sp² hybridized boron atoms forming triangular units.
- 2 sp³ hybridized boron atoms forming tetrahedral units.
- The sodium ions balance the negative charges from the boron atoms.

### Step 7: Water of Crystallization
The `8H2O` indicates that there are 8 water molecules associated with the structure, which are typically present in the crystal lattice and do not affect the bonding of the main structure.

### Final Structure Summary
The structure of `Na2[B4O5(OH)4]·8H2O` contains:
- 2 triangular units (sp² hybridized)
- 2 tetrahedral units (sp³ hybridized)