Bonding
Metallic Bonding
"Sea of electrons" — delocalized bonding among metal atoms gives unique properties
Metallic bonding is the bonding model for metals — positively charged metal cations held in fixed positions by a "sea" of delocalized valence electrons. Unlike ionic (electron transfer) or covalent (localized sharing), metallic bonding has electrons free to move throughout the lattice. Explains: high electrical conductivity (mobile electrons), thermal conductivity, ductility/malleability (cations can shift without breaking bonds), shine (electrons interact with light), high melting points. Strength varies: Hg (BP -39°C, weak) to W (BP 3422°C, very strong).
- ModelCation lattice + delocalized electron sea
- Key featureMobile electrons enable conductivity
- Strength rangeHg (weak) to W (very strong)
- PropertiesConductive, malleable, ductile, shiny, dense
- Bond characterNon-directional (unlike covalent)
- Crystal structuresBCC, FCC, HCP (close-packed)
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Why metallic bonding matters
- Engineering materials. Steel, aluminum, alloys.
- Electrical wiring. Conductivity from electron sea.
- Construction. Strength, ductility.
- Heat transfer. Thermal conductivity.
- Decoration. Reflective shine.
- Currency. Coins (mostly metals).
- Catalysis. Surface reactions on transition metals.
Common misconceptions
- Metallic bonds same as covalent. Delocalized vs localized.
- Electron sea is literal liquid. Quantum mechanical bands.
- All metals shiny. Sodium oxidizes; many darken.
- Ductile = malleable. Different (drawn into wires vs hammered into sheets).
- Pure metals are strongest. Often alloys are stronger.
- Metals all conduct same. Conductivity varies widely (Cu high, Bi low).
Frequently asked questions
How does metallic bonding work?
Metal atoms have low ionization energies — easily lose valence electrons. In solid metal: each atom contributes 1-3 valence electrons to a shared "sea." Result: lattice of metal cations (positive) bathed in mobile electrons (negative). Cations attracted to electron sea — bonding. No specific atom owns specific electron — fully delocalized.
Why are metals conductive?
Electron sea is mobile. Apply voltage → electrons drift toward positive electrode → current flows. Same mobility explains thermal conductivity (electrons carry heat), light reflection (interact with electromagnetic radiation), ductility (electrons reorganize to maintain bonding when atoms shift).
Why are metals malleable?
Non-directional bonding. Push metal — atoms slide past each other; electron sea reorganizes to maintain bonding. Doesn't break. Compare ionic crystals (NaCl): hit them and they shatter — sliding ions creates like-charge repulsion. Metals: sliding cations still surrounded by electrons. Property: deformable.
Why are some metals harder than others?
Bond strength. Depends on: number of valence electrons donated (more = stronger), size of cation (smaller = stronger), packing efficiency (close-packed = stronger). Sodium (1 e-, large): soft, low BP (98°C). Tungsten (6 e-, smaller): very hard, BP 3422°C. Mercury: anomalously weak — relativistic effects.
What's an alloy?
Mixture of metals (or metal + nonmetal) with metallic bonding. Two types: (1) Substitutional — different-sized atoms replace some host atoms (brass = Cu + Zn). (2) Interstitial — small atoms fit between host atoms (steel = Fe + C). Often stronger than pure metals (different sizes prevent slipping). Common: bronze, brass, steel, sterling silver.
How does metallic bonding compare to other bonds?
Different model. Ionic: localized electrostatic (cation + anion). Covalent: localized sharing (electron pair between specific atoms). Metallic: delocalized; electrons free to move; bonding without specific partners. All strong bonds (>100 kJ/mol typically) but very different properties — explains why metals so distinct.
What about transition metals?
d-electrons can also participate in bonding sea. Often stronger metallic bonds. Higher melting points: Fe 1538°C, Mo 2622°C, W 3422°C. Color: d-d transitions in some transition metals (Au gold, Cu reddish). Magnetic: Fe, Ni, Co ferromagnetic due to unpaired d electrons in bands.