Which of the following species are hypervalent ?
`(I) ClO_(4)^(-) " "(II) BF_(3)`
`(III) SO_(4)^(-2)" "(IV) CO_(3)^(-2)`

Options

A. I, II, III
B. I, III
C. III, IV
D. I, III, IV

Answer

To determine which of the given species are hypervalent, we need to analyze the electron count around the central atom in each species. A hypervalent species is defined as one that has a central atom with more than 8 valence electrons.

Let's analyze each species one by one:

### Step 1: Analyze ClO₄⁻ (Chlorate Ion)
1. **Structure**: The chlorate ion has a central chlorine atom bonded to four oxygen atoms.
2. **Bonding**: The structure can be represented as:
- Cl = O (double bond)
- Cl - O (double bond)
- Cl - O (double bond)
- Cl - O (single bond with a negative charge on one oxygen)
3. **Electron Count**:
- Each double bond contributes 4 electrons (2 from each bond).
- The single bond contributes 2 electrons.
- Therefore, total electrons = 4 (from 3 double bonds) + 2 (from single bond) + 1 (from the negative charge) = 13 electrons.
4. **Conclusion**: Since chlorine has more than 8 electrons, ClO₄⁻ is hypervalent.

### Step 2: Analyze BF₃ (Boron Trifluoride)
1. **Structure**: Boron trifluoride has a central boron atom bonded to three fluorine atoms.
2. **Bonding**: The structure can be represented as:
- F - B - F
- F
3. **Electron Count**:
- Each bond contributes 2 electrons.
- Therefore, total electrons = 2 (from each bond) x 3 = 6 electrons.
4. **Conclusion**: Since boron has only 6 electrons, BF₃ is not hypervalent; it is electron-deficient.

### Step 3: Analyze SO₄²⁻ (Sulfate Ion)
1. **Structure**: The sulfate ion has a central sulfur atom bonded to four oxygen atoms.
2. **Bonding**: The structure can be represented as:
- S = O (double bond)
- S = O (double bond)
- S - O (single bond with a negative charge)
- S - O (single bond with a negative charge)
3. **Electron Count**:
- Each double bond contributes 4 electrons (2 from each bond).
- Each single bond contributes 2 electrons.
- Therefore, total electrons = 4 (from 2 double bonds) + 2 (from 2 single bonds) + 2 (from the two negative charges) = 12 electrons.
4. **Conclusion**: Since sulfur has more than 8 electrons, SO₄²⁻ is hypervalent.

### Step 4: Analyze CO₃²⁻ (Carbonate Ion)
1. **Structure**: The carbonate ion has a central carbon atom bonded to three oxygen atoms.
2. **Bonding**: The structure can be represented as:
- C = O (double bond)
- C - O (single bond with a negative charge)
- C - O (single bond with a negative charge)
3. **Electron Count**:
- Each double bond contributes 4 electrons.
- Each single bond contributes 2 electrons.
- Therefore, total electrons = 4 (from the double bond) + 2 (from each single bond) x 2 = 8 electrons.
4. **Conclusion**: Since carbon has exactly 8 electrons, CO₃²⁻ is not hypervalent.

### Final Conclusion
The hypervalent species from the given options are:
- ClO₄⁻ (1)
- SO₄²⁻ (3)

Thus, the correct answer is **(I) and (III)**.