Example 1
Explain why a copper wire conducts without its atoms flowing down the wire.
Delocalised electrons move through the solid lattice and carry current; the metal centres remain near fixed positions.
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Year 11 · SACE Stage 1
Metallic bonding and covalent networks
Apply extended-structure models to conductivity, hardness and deformation.
Method and worked examples
Metallic bonding is attraction between positive metal centres and delocalised valence electrons. Mobile electrons explain electrical conductivity in a solid metal. When layers slide, attraction to the shared electron cloud remains, explaining malleability. Alloys can have different hardness from pure metals because atoms of different sizes disrupt regular layer movement; conductivity and corrosion properties may change too.
Diamond has four covalent bonds around each carbon in a three-dimensional network. Graphite has three covalent bonds around each carbon in sheets, with delocalised electrons that conduct along the sheets. Weaker attractions between sheets allow them to slide. Silicon dioxide is also a covalent network. Network formulae give atom ratios rather than isolated molecular sizes; graphite and diamond are allotropes because both contain only carbon.
Example 1
Example 2
Why can graphite act as a pencil material while diamond is hard?
Graphite sheets can slide because interlayer attractions are weaker; diamond has strong covalent connections in three dimensions.
Watch out: In solid metals, delocalised electrons are the mobile charge carriers.