Ionic Bonding
7 marks · HardSodium chloride (NaCl) is a typical ionic compound. The arrangement of ions in its structure and the structure's properties explain many features of ionic solids.
Describe how the ions are arranged in the giant ionic lattice of sodium chloride.
Explain why sodium chloride has a high melting point, referring to its structure.
State one feature of the overall appearance of pure sodium chloride crystals and relate it to the arrangement of ions in its lattice.
Give one other property (besides melting point) that is explained by the structure of giant ionic lattices, and state how the arrangement of ions accounts for it.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Ions are arranged in a regular three-dimensional lattice; each Na+ is surrounded by 6 Cl- ions and each Cl- is surrounded by 6 Na+ ions in a repeating pattern. · must show regular/lattice/3D structure, each ion surrounded by 6 oppositely charged ions
(b) Sodium chloride has a high melting point because strong electrostatic forces of attraction between oppositely charged ions in the giant lattice require a lot of energy to overcome. · must show strong electrostatic forces, need much energy to break
(c) Sodium chloride is crystalline. This is because the regular arrangement of ions in the lattice leads to a structure that forms crystals. · must show crystalline/crystals, due to regular/repeating arrangement
(d) Brittleness (or does not conduct electricity when solid, but does when molten or dissolved): The fixed positions of ions in the lattice explain the property. · must show conductivity or brittleness explained by fixed ions in lattice
Common mistakes: describing sodium chloride as a molecule; saying the ions are in pairs or molecules; not linking strong forces to high melting point; failing to relate crystalline appearance to arrangement
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Describes regular lattice/3D repeating structure
B2 (a) · 1 mark · States each Na+ ion is surrounded by 6 Cl- ions and vice versa (or describes correct coordination number)
B3 (b) · 1 mark · Links high melting point to strong electrostatic forces between oppositely charged ions
B4 (b) · 1 mark · States a lot of energy is needed to break these forces
B5 (c) · 1 mark · Identifies sodium chloride as crystalline (forms crystals)
B6 (c) · 1 mark · Relates crystallinity to regular/repeating arrangement of ions
B7 (d) · 1 mark · Names another physical property (e.g., electrical conductivity or brittleness) and correctly relates it to structure
Worked solution
(a) In a giant ionic lattice of sodium chloride, ions are arranged in a three-dimensional repeating pattern. Each sodium ion (Na+) is surrounded by six chloride ions (Cl-), and each chloride ion is surrounded by six sodium ions. This pattern repeats throughout the structure.
(b) Sodium chloride has a high melting point because the lattice is held together by strong electrostatic forces between oppositely charged ions. Breaking these forces requires a large amount of energy, so the melting point is high.
(c) Pure sodium chloride is crystalline. The regular, repeating arrangement of ions in the lattice results in the material forming crystals.
(d) Another property is brittleness. When a force is applied, like-charged ions may be forced next to each other, leading to repulsion and causing the crystal to break. Alternatively, sodium chloride does not conduct electricity as a solid because the ions are fixed in position in the lattice.