Pure Metals vs. Alloys: Pure metals have uniform layers that slide easily, making them soft; alloys contain different-sized atoms that disrupt these layers, making them much harder.
Metallic vs. Ionic Conductivity: Metals conduct in the solid state via electrons, whereas ionic compounds only conduct when molten or aqueous via mobile ions.
| Property | Pure Metal | Alloy |
|---|---|---|
| Structure | Uniform layers | Disrupted layers |
| Hardness | Relatively soft | Hard and strong |
| Sliding | Easy | Difficult |
Drawing Requirements: When asked to draw a metallic lattice, always include at least two layers of ions, label the 'positive ions' and 'delocalised electrons', and ensure ions are touching to show the solid state.
Explaining Trends: If comparing melting points (e.g., Na vs. Mg), always mention both the increase in ion charge ( to ) and the increase in the number of delocalised electrons.
State of Matter: Remember that metals are the only giant structures that conduct electricity in the solid state; use this as a diagnostic feature in identification questions.
Terminology Precision: Avoid saying 'metal atoms' are in the lattice; use 'positive metal ions' or 'cations' to reflect the loss of valence electrons.
Directionality: Students often mistakenly think metallic bonds break during deformation; in reality, the sea of electrons maintains the bond during sliding, which is why metals don't shatter like ionic crystals.
Electron Source: A common error is forgetting that the number of delocalised electrons is determined by the group number of the metal (e.g., Group 2 metals provide 2 electrons per atom).
Thermal vs. Electrical: Do not confuse the two; while both involve delocalised electrons, thermal conductivity also significantly involves the vibration of the cations themselves.
Periodicity: Metallic bond strength generally increases across a period (e.g., Na to Al) as the charge density of the ions increases and more electrons are delocalised.
Material Science: The principles of alloying are used to engineer specific properties, such as increasing the corrosion resistance or tensile strength of structural materials like steel.
State Changes: The high boiling points of metals relative to their melting points indicate that while layers can slide easily (melting), completely separating the ions from the electron sea (boiling) requires massive energy.
