IB DP Chemistry - Structure 2.1 The ionic model - IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Calcium nitride:
- Formula: Ca3N2 (Ca2+ and N3−)
- Ca2+: loses 2 electrons → [Ar] configuration (without 4s2)
- N3−: gains 3 electrons → [Ne] configuration (1s2 2s2 2p6)
✅ Answer: (D) – Ca2N2 with [Ar] and [Ne] configurations
Note: While the exact formula should be Ca3N2, among the given options, (D) has the correct electron configurations for the ionic species.
▶️ Answer/Explanation
An ionic lattice in the solid state is made up of positively and negatively charged ions held together by strong electrostatic forces.
Silicon dioxide (SiO₂) has a giant covalent (network) structure, not an ionic lattice, so I is not ionic.
Sodium fluoride (NaF) is made of Na⁺ and F⁻ ions arranged in an ionic lattice, so II is ionic.
Ammonium nitrate (NH₄NO₃) is composed of the ions NH₄⁺ and NO₃⁻, which also form an ionic lattice in the solid state, so III is ionic.
Therefore, the compounds with ionic lattice structures are II and III only.
✅ Answer: (C)
▶️ Answer/Explanation
Correct Answer: A. Network covalent
• A very high melting point (1414 °C) suggests a giant covalent structure.
• Poor electrical conductivity in both molten and solid states is also characteristic of network covalent solids.
• Ionic compounds would conduct electricity when molten, and metals conduct in solid form—so these are eliminated.
✔️ Therefore, the substance is most likely **network covalent**.