Metallic bonding explains why metals such as copper, aluminum, iron, and sodium share many familiar properties. In a metal, atoms pack together in an orderly lattice, but their outer valence electrons are not held by just one atom. These electrons become delocalized, forming a mobile electron sea around positive metal ion cores.
This model helps explain why metals conduct electricity, bend without shattering, and reflect light to look shiny.
The attraction between the positive metal cations and the negative delocalized electrons holds the metal together. Because the electrons can move throughout the lattice, they can carry electric charge and thermal energy efficiently. When a metal is hammered or drawn into a wire, layers of positive ion cores can slide past each other while the electron sea keeps attracting them.
Metallic bonding is different from ionic bonding, where electrons are transferred between different atoms, and covalent bonding, where electrons are shared in localized pairs.
Key Facts
- Metallic bonding is the electrostatic attraction between positive metal ion cores and delocalized valence electrons.
- In the electron-sea model, metal atoms form M+ ion cores surrounded by mobile electrons.
- Electrical conductivity occurs because delocalized electrons can move through the metal when a voltage is applied.
- Malleability and ductility occur because metal ion layers can slide while the electron sea maintains attraction.
- Metals are shiny because mobile electrons absorb and re-emit visible light at the surface.
- Stronger metallic bonding generally occurs with more delocalized electrons and smaller or more highly charged metal cations.
Vocabulary
- Metallic bond
- A metallic bond is the attraction between positive metal ion cores and a shared sea of delocalized electrons.
- Delocalized electron
- A delocalized electron is an electron that is not attached to one specific atom and can move through the metal lattice.
- Metal cation
- A metal cation is a positive ion core formed when a metal atom contributes its valence electrons to the electron sea.
- Malleability
- Malleability is the ability of a material to be hammered or pressed into thin sheets without breaking.
- Ductility
- Ductility is the ability of a material to be stretched or drawn into a wire without snapping.
Common Mistakes to Avoid
- Thinking metallic bonds are the same as covalent bonds is wrong because metallic electrons are delocalized across many atoms, not shared as fixed pairs between two atoms.
- Saying metals conduct because positive ions move is wrong because the metal ion cores mostly vibrate in place while delocalized electrons carry charge.
- Drawing electrons stuck between only two metal atoms is wrong because the electron-sea model shows electrons spread throughout the whole lattice.
- Assuming all metals have identical strength is wrong because metallic bond strength depends on ion charge, ion size, and the number of delocalized electrons.
Practice Questions
- 1 Magnesium contributes 2 valence electrons per atom to metallic bonding. How many delocalized electrons are available in a sample containing 5.0 x 10^22 magnesium atoms?
- 2 A piece of aluminum contains 3.0 x 10^23 atoms, and each aluminum atom contributes 3 valence electrons. How many delocalized electrons are in the electron sea?
- 3 Explain why a metal wire can conduct electricity while a solid ionic crystal usually cannot, using the motion of charged particles in each substance.