Predicting Structures (Edexcel A Level Chemistry): Revision Note

Bonding & structure

The table below shows the physical properties of substances X, Y and Z

Which one of the following statements about X and Y is completely true?

Statement 1: X has a giant ionic structure, Y has a giant molecular structure, Z is a metal

Statement 2: X is a metal, Y has a simple molecular structure, Z has a giant molecular structure

Statement 3: X is a metal, Y has a simple molecular structure, Z has a giant ionic structure

Statement 4: X has a giant ionic structure, Y has a simple molecular structure, Z is a metal

Answer

The correct answer is Statement 4

• The relatively high melting point, solubility in water and electrical conductivity when molten suggest that X is a giant ionic structure.

  • The low melting point of Y suggests that little energy is needed to break the lattice which corresponds to a simple molecular structure. This is further supported by the low electrical conductivity and its being almost insoluble in water.

  • Compound Z has a very high melting point which is characteristic of either metallic or giant molecular lattices, however since it conducts electricity, compound Z must be a giant metallic lattice.

Bonding & structure

Compound X has the following properties:

What is the most probable structure of X?

A. Network covalent

B. Polar covalent molecule

C. Ionic lattice

D. Metallic lattice

Answer:

The correct option is A

• A high melting point is characteristic of a giant structure, which could be metallic, ionic or covalent

  • The poor conductivity as a liquid and solid would match a giant covalent or network covalent structure