Which of the following species are hypervalent?
`(A) ClO_(4)^(-)" "(B)BF_(3)`
`(C ) SO_(4)^(-2)" "(D)CO_(3)^(-2)`

Options

A. A, B, C
B. C, D
C. A, C
D. A, B

Answer

To determine which of the given species are hypervalent, we need to analyze each species and check if they have more than eight electrons in their valence shell. Hypervalent species are those that can accommodate more than eight electrons due to the presence of d-orbitals.

Let's evaluate each option step by step:

### Step 1: Analyze ClO₄⁻ (Chlorate Ion)
1. **Count Valence Electrons**: Chlorine (Cl) has 7 valence electrons, and each oxygen (O) has 6 valence electrons. The ion has a -1 charge, contributing an additional electron.
- Total = 7 (Cl) + 4 × 6 (O) + 1 (charge) = 7 + 24 + 1 = 32 electrons.
2. **Lewis Structure**: Draw the Lewis structure. Chlorine is the central atom bonded to four oxygen atoms. Each oxygen forms a double bond with chlorine, and one oxygen carries a negative charge.
3. **Count Electrons Around Cl**: Chlorine is surrounded by 12 electrons (4 bonds).
4. **Conclusion**: Since chlorine has more than 8 electrons, ClO₄⁻ is hypervalent.

### Step 2: Analyze BF₃ (Boron Trifluoride)
1. **Count Valence Electrons**: Boron (B) has 3 valence electrons, and each fluorine (F) has 7 valence electrons.
- Total = 3 (B) + 3 × 7 (F) = 3 + 21 = 24 electrons.
2. **Lewis Structure**: Draw the Lewis structure. Boron is the central atom bonded to three fluorine atoms.
3. **Count Electrons Around B**: Boron is surrounded by 6 electrons (3 bonds).
4. **Conclusion**: Since boron has 6 electrons, BF₃ is not hypervalent.

### Step 3: Analyze SO₄²⁻ (Sulfate Ion)
1. **Count Valence Electrons**: Sulfur (S) has 6 valence electrons, and each oxygen (O) has 6 valence electrons. The ion has a -2 charge, contributing 2 additional electrons.
- Total = 6 (S) + 4 × 6 (O) + 2 (charge) = 6 + 24 + 2 = 32 electrons.
2. **Lewis Structure**: Draw the Lewis structure. Sulfur is the central atom bonded to four oxygen atoms, with some double bonds.
3. **Count Electrons Around S**: Sulfur is surrounded by 12 electrons (4 bonds).
4. **Conclusion**: Since sulfur has more than 8 electrons, SO₄²⁻ is hypervalent.

### Step 4: Analyze CO₃²⁻ (Carbonate Ion)
1. **Count Valence Electrons**: Carbon (C) has 4 valence electrons, and each oxygen (O) has 6 valence electrons. The ion has a -2 charge, contributing 2 additional electrons.
- Total = 4 (C) + 3 × 6 (O) + 2 (charge) = 4 + 18 + 2 = 24 electrons.
2. **Lewis Structure**: Draw the Lewis structure. Carbon is the central atom bonded to three oxygen atoms, with one double bond and two single bonds.
3. **Count Electrons Around C**: Carbon is surrounded by 8 electrons (4 bonds).
4. **Conclusion**: Since carbon has exactly 8 electrons, CO₃²⁻ is not hypervalent.

### Final Conclusion
The hypervalent species among the options are:
- (A) ClO₄⁻
- (C) SO₄²⁻

### Answer:
The hypervalent species are (A) ClO₄⁻ and (C) SO₄²⁻.

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