Metallic Bonding

What is metallic bonding?

• Metal atoms are tightly packed together in lattice structures

• When the metal atoms are in lattice structures, the electrons in their outer shells are free to move throughout the structure

  • The free-moving electrons are called ‘delocalised' electrons and they are not bound to their atom

• When the electrons are delocalised, the metal atoms become positively charged

• The positive charges repel each other and keep the neatly arranged lattice in place

• There are very strong electrostatic forces between the positive metal centres and the ‘sea’ of delocalised electrons

What are the properties of metals?Malleability

• Metals are malleable (can be hammered into sheets) and ductile (can be drawn into wires)

• This is because the layers of metal ions can slide over each other when a force is applied

• The delocalised electrons allow the metal to retain its structure without breaking the bonds

Strength

• Metals are typically strong and hard due to:

  • The strong electrostatic attraction between cations and electrons

  • The closely packed structure of the metal ions

Electrical conductivity

• Metals can conduct electricity when in the solid or liquid state

  • In the solid and liquid states, there are mobile electrons which can freely move around and conduct electricity

• When a potential difference is applied to a metallic lattice, the delocalised electrons repel away from the negative terminal and move towards the positive terminal

  • As the number of outer electrons increases across a period, the number of delocalised charges also increases:

    • Na = 1 outer electron

    • Mg = 2 outer electrons

    • Al = 3 outer electrons

  • Therefore, the ability to conduct electricity also increases across a period

  • Thermal conductivity

    • Metals are good thermal conductors due to the behaviour of their cations and their delocalised electrons

      • When metals are heated, the cations in the metal lattice vibrate more vigorously as their thermal energy increases

        • These vibrating cations transfer their kinetic energy as they collide with neighbouring cations, effectively conducting heat

      • The delocalised electrons are not bound to any specific atom within the metal lattice and are free to move throughout the material

        • When the cations vibrate, they transfer kinetic energy to the electrons

        • The delocalised electrons then carry this increased kinetic energy and transfer it rapidly throughout the metal, contributing to its high thermal conductivity.

    Melting and boiling point

    • Metals have high meltingand boiling points

      • This is due to the strong electrostatic forces of attractionbetween the cations and delocalised electrons in the metallic lattice

      • These require large amounts of energy to overcome 

      • As the number of mobile charges increases across a period, the melting and boiling points increase due to stronger electrostatic forces 

    Uses of metals

    • The metal chosen for a particular job can be based on considering the following list of metal properties:

      • Malleability / ductility

      • Melting / boiling point

      • Density

      • Reactivity

      • Electrical conductivity

      • Strength

      • Toxicity

      • Lustre

      • Thermal conductivity

      • Strength-to-weight ratio

      • Corrosion resistance

      • Sonority

    • For example:

      • Aluminium is used in food cans because it is non-toxic and resistant to corrosion and acidic food stuffs

      • Copper is used in electrical wiring because it is a good electrical conductor and malleable / ductile

      • Stainless steel is used for cutlery as