Metallic Bonding
Section: 2. Atoms, Elements & Compounds | Syllabus: Cambridge IGCSE Chemistry (0620)
What is Metallic Bonding?
Metallic bonding is the electrostatic attraction between the positive ions in a giant metallic lattice and a "sea" of delocalized electrons.
- Each metal atom releases its outer-shell electron(s), becoming a positive ion (cation)
- These released electrons do not belong to any one atom - they are delocalized, free to move throughout the whole structure
- The positive metal ions arrange themselves in a regular giant lattice, held together by strong electrostatic attraction to the surrounding sea of electrons
The positive metal ions sit in a fixed lattice while the delocalized electrons move freely through the whole structure, like a sea surrounding them
Properties of Metals Explained by Structure
Good Electrical Conductivity
- The delocalized electrons are free to move throughout the structure
- When a voltage is applied, these electrons flow and carry electric charge - this works in both the solid and molten states, since it is the electrons (not the fixed metal ions) that move
Malleability and Ductility
- Metallic bonding is non-directional - it acts equally in all directions, not between fixed pairs of atoms
- When force is applied, layers of metal ions can slide over one another into new positions
- The sea of delocalized electrons simply flows to surround the ions in their new positions, so strong bonding is maintained
- This is why metals can be hammered into sheets (malleable) or drawn into wires (ductile) without shattering - unlike ionic compounds, where sliding brings like charges together and causes the crystal to split
Worked Example: Malleability vs Brittleness
- Question: explain why metals are malleable, while ionic compounds are brittle. [3]
- Answer: in a metal, when layers of ions slide, the delocalized "sea" of electrons moves with them and continues to hold the structure together, so the metal simply changes shape [2]; in an ionic compound, sliding brings ions of the same charge next to each other, which repel strongly and cause the crystal to shatter [1]
Common Mistakes
- ❌ Thinking metals conduct electricity because the metal ions move
- ✓ the positive metal ions stay in fixed lattice positions - it is the delocalized electrons that are free to move and carry the current
- ❌ Thinking an alloy is a compound
- ✓ an alloy (e.g. steel, brass) is a mixture of a metal with one or more other elements, not a new chemically bonded compound - atoms of different sizes disrupt the regular layers, making it harder for them to slide, which is why alloys are generally harder than pure metals
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