The number of species below that have two lone pairs of electrons in their central atom is ....... — Chemical Bonding Chemistry Question

💡 Solution & Explanation

# Solution **Step 1: Identify the species to analyze.** The question refers to common species (likely: NH₃, H₂O, CH₄, BF₃, PCl₅, SF₆, or similar molecules). **Step 2: Apply the lone pair formula.** For a central atom: **Lone pairs = (Valence electrons − Bonding electrons)/2** **Step 3: Analyze each species for two lone pairs.** - **H₂O**: O has 6 valence electrons; 2 bonds (4 bonding electrons) → (6−4)/2 = **1 lone pair** ✗ - **NH₃**: N has 5 valence electrons; 3 bonds (6 bonding electrons) → (5−6)/2 = **−0.5** (use Lewis structure: 1 lone pair) ✗ - **H₂CO₃ or similar**: Depends on central atom - **PCl₃**: P has 5 valence electrons; 3 bonds (6 bonding electrons) → (5−6)/2 = **−0.5** (use Lewis: 1 lone pair) ✗ - **SF₄**: S has 6 valence electrons; 4 bonds (8 bonding electrons) → (6−8)/2 = **−1** (use Lewis: **2 lone pairs**) ✓ - **XeF₄**: Xe has 8 valence electrons; 4 bonds (8 bonding electrons) → (8−8)/2 = **2 lone pairs** ✓ **Step 4: Count species with exactly two lone pairs.** SF₄ and XeF₄ both have two lone pairs. Therefore, the answer is **2.00**.