The halite unit cell consists of ____.

Question

BlackTom AI · Accepted Answer

Halite is the mineral form of sodium chloride (NaCl): its unit cell contains sodium and chlorine ions arranged in the rock-salt (NaCl) structure.

1. Relevant knowledge points and concepts
- Crystal structure type: rock-salt (NaCl) structure, which is based on two interpenetrating face-centered cubic (fcc) lattices.
- Constituents: Na+ (sodium cations) and Cl− (chloride anions).
- Coordination: Each ion has an octahedral coordination number of 6 (each Na+ is surrounded by 6 Cl− and vice versa).
- Stoichiometry: 1:1 ratio of Na+ to Cl−; four formula units per unit cell.

2. Complete reasoning process (step by step)
- Place one species (say Cl−) on the fcc lattice positions (corners and face centers).
- The other species (Na+) occupies the octahedral holes (edge-centers and the body center), forming an interpenetrating fcc lattice displaced by (1/2, 0, 0) etc.
- This arrangement ensures electrostatic stability and close packing consistent with ionic sizes.

3. Intermediate counting steps
- Cl− contribution: 8 corner atoms × 1/8 each = 1; 6 face-centered atoms × 1/2 each = 3; total Cl− per unit cell = 4.
- Na+ contribution: 12 edge-centered atoms × 1/4 each = 3; 1 body-centered atom × 1 = 1; total Na+ per unit cell = 4.
- Thus there are 4 Na+ and 4 Cl− per unit cell, preserving the 1:1 stoichiometry.

4. Why the correct answer is correct
- The halite unit cell is ionic, built from discrete Na+ and Cl− ions in a cubic lattice with octahedral coordination. Therefore the correct description is “Sodium and Chlorine ions.”

5. Why other possible answers would be incorrect
- “NaCl molecules” is incorrect because the solid is an extended ionic lattice, not discrete neutral NaCl molecules.
- “Only sodium ions” or “only chlorine ions” are incorrect because both oppositely charged ions are present in equal numbers.
- Any suggestion of covalent atoms or a different stoichiometry contradicts the well-established NaCl rock-salt structure.

6. Conclusion
The unit cell of halite consists of sodium and chlorine ions (Sodium and Chlorine ions), which matches the provided correct answer.

The halite unit cell consists of ____.单项选择题

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