Recognising metallic giant structures from diagrams
Bonding, structure, and the properties of matter • Chemical bonds
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Definition of a metallic giant structure
A metallic giant structure consists of a regular three-dimensional lattice of positive metal ions. Electrons from outer shells become delocalised and form a mobile 'sea' that surrounds the ions. The structure extends throughout the solid and contains no discrete molecules, so the whole sample behaves as a continuous network of ions and delocalised electrons. Limiting factors include the type of metal and presence of alloys. Alloys contain different metal atoms that disrupt the regular lattice and alter properties. Small clusters or isolated atoms in a matrix do not form a true giant metallic structure.
Diagram features that identify metallic bonding
Diagrams that show metallic bonding present regularly spaced positive ions (often labelled with the element symbol and a positive charge) arranged in a lattice. Mobile or delocalised electrons appear as free electrons, dots, or a shaded electron 'sea' not associated with any specific ion. Absence of distinct covalent bonds or separated molecules indicates a metallic giant structure. Limiting visual cues include the scale and labelling. Diagrams that omit charges or electrons require interpretation of context, such as grouping of many identical atoms in a repeating pattern, to infer metallic bonding.
Cause: delocalised electrons - Effect: conductivity and thermal conduction
Delocalised electrons move freely through the lattice and carry electric charge when a potential difference applies. The presence of mobile electrons causes metals to conduct electricity in solid and molten states. The same electron mobility transfers kinetic energy quickly through the structure, causing high thermal conductivity. Limiting factors include temperature and impurity. Increased temperature raises ion vibration, which can scatter electrons and reduce electrical conductivity. Impurities and alloying elements disrupt electron flow and alter conductivity.
Cause: non-directional metallic attraction - Effect: malleability and ductility
Electrostatic attraction between positive ions and the delocalised electron cloud acts in all directions and does not rely on fixed bonds between specific ions. When layers of ions slide, the electron sea repositions to maintain attraction, allowing metals to deform without shattering. This cause produces malleability (hammering into sheets) and ductility (stretching into wires). Limiting factors include brittle intermetallic compounds and impurities. Some metallic materials become brittle if directional bonding or large atomic size differences appear, reducing malleability.
Cause: strong electrostatic attraction and close packing - Effect: high melting and boiling points
Strong attraction between many positive ions and the delocalised electrons requires large input of energy to overcome. Close-packed lattices increase the number of attractions per ion, raising melting and boiling points. Transition metals often show higher melting points due to more delocalised electrons from d-orbitals. Limiting factors include metallic radius and electron density. Larger atoms with lower electron density and weaker attraction can have lower melting points. Alloying and crystal defects also modify melting behaviour.
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