States of Matter: Question 10

Worked solution

Step 1: Consider the melting point

A high melting point rules out a simple molecular lattice (option C), since simple molecular solids are held together only by weak intermolecular forces and typically melt well below room temperature, or at most a few hundred degrees Celsius.

Step 2: Consider the electrical conductivity

Z conducts electricity both as a solid and when molten. This immediately rules out:

• A giant ionic lattice (option A): the ions are fixed in position in the solid lattice and cannot move, so an ionic solid does not conduct electricity as a solid, only once molten (or dissolved), when the ions become free to move.
• A giant covalent lattice (option D): most giant covalent structures, such as diamond, have no delocalised electrons or mobile charge carriers and do not conduct electricity in either state (a small number of exceptions, such as graphite, conduct only because of a special layered structure, which is not implied here).

Only a giant metallic lattice has delocalised (“sea of”) electrons that are free to move throughout the structure at all times, allowing it to conduct electricity both as a solid and when molten.

Step 3: Consider malleability

The fact that Z can be hammered into different shapes without shattering (it is malleable) confirms a metallic lattice: the positive metal ions are arranged in layers within a delocalised sea of electrons, so when a force is applied, layers of ions can slide over one another while remaining surrounded by (and bonded through) the mobile electrons. The metallic bonding is not broken, so the solid deforms rather than shattering. An ionic lattice, by contrast, is brittle: displacing one layer of ions causes ions of the same charge to align, and strong repulsion shatters the lattice.

Final answer

• The properties of Z (high melting point, conduction as both a solid and a liquid, and malleability) match a $\boxed{\text{giant metallic lattice}}$, option B.