02. Crystal Structures of Ionic Substances

What are the 2 ionic lattice examples?

Sodium chloride and Caesium chloride

Draw sodium chloride

Yes

Draw caesium chloride

Yes

What is the coordination number of sodium chloride?

6:6

What is the coordination number of caesium chloride?

8:8

Describe the structure of sodium chloride?

Each Na⁺ ion surrounded by 6 Cl^- ions with sodium in the centre and chlorides extending in 3 dimensional planes, When drawn in 2D sodium is front centre (face centred) and each Cl^- surrounded by Na⁺ in the same configuration

What is a coordination number?

Number of oppositely charged ions immediately around an ion

What is the coordination number of caesium chloride?

8:8

Describe the structure of caesium chloride?

Each Cs⁺ ion surrounded by 8 Cl^- at the corners with Cs⁺ in the centre (hence body centred), Cl^- ion is surrounded by 8 Cs⁺ ions

Why do sodium and caesium have different coordinate numbers and structures?

Sodium is small so only 6 oppositely charged ions can pack around it, Caesium is larger so 8 can pack around it

What are common mistakes?

Ions called atoms/molecules, Sodium ions bonded to 6 chloride ions -> It’s an electrostatic attraction