Ionic & Metallic Bonding & Structure

• Evidence of ions: electron density maps, melting/boiling points, electrical conductivity, solubility, and electrolysis all provide proof that ions actually exist.
• Ionic bonding & structure: how electrons transfer from metals to non-metals to form oppositely charged ions, which then pack into giant ionic lattices held together by electrostatic attraction.
• Dot-and-cross diagrams: how to draw the electron transfer for compounds like NaCl, MgO, CaF₂, Li₃N, and Al₂O₃.
• Ionic bond strength: how atomic radius and ionic radius change across periods and groups, and why this affects bond strength (charge density).
• Polarisation: how a cation can distort an anion's electron cloud, introducing "covalent character" into an otherwise ionic bond.
• Metallic bonding & lattices: the "sea of delocalised electrons" model, and how it explains metals' physical properties (conductivity, malleability, high melting points).

Giant Ionic Lattices

Think of an ionic bond like a very committed, permanent handshake between a positively charged metal ion (a cation) and a negatively charged non-metal ion (an anion). The metal atom has given away electrons (becoming positive), and the non-metal has taken them (becoming negative).

Unlike a covalent bond, which only pulls two specific atoms together, an ionic bond pulls in every direction at once. This means ions don't just pair up — they stack into a huge, repeating 3D pattern called a giant ionic lattice (also called a giant ionic structure). Every positive ion is surrounded by negative ions, and vice versa, like a 3D checkerboard.

Electron density maps are one piece of hard evidence for ions. These maps show where electrons are most likely to be found. For NaCl, the map shows two separate "islands" of electron density (one smaller, around Na⁺, one larger, around Cl⁻) with the density dropping to zero in between. This gap is exactly what you'd expect if electrons have been completely transferred from Na to Cl — there's no "shared" electron cloud like you'd see in a covalent bond.

Melting & Boiling Point

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The bigger the ionic charge, the higher the melting point, because the electrostatic attraction is stronger. Compare:

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