Properties of Metals & Their Uses (HL IB Chemistry)

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

Metallic bonding diagram

The structure of metallic bonding has positive metal ions suspended in a ‘sea’ of delocalised electrons

What are the properties of metals?

Malleability

• Metallic compounds are malleable
• When a force is applied, the metal layers can slide
• The attractive forces between the metal ions and electrons act in all directions
• So when the layers slide, the metallic bonds are re-formed
• The lattice is not broken and has changed shape

How metals are malleable diagram

Atoms are arranged in layers so the layers can slide when force is applied

Strength

• Metallic compounds are strong and hard
  • Due to the strong attractive forces between the metal ions and delocalised electrons

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:
    • Sodium = 1 outer electron
    • Magnesium = 2 outer electrons
    • Aluminium = 3 outer electrons
  • Therefore, the ability to conduct electricity also increases across a period

How metals conduct electricity diagram

The delocalised electrons move towards the positive terminal when a potential difference is applied

• Since the bonding in metals is non-directional, it does not really matter how the cations are oriented relative to each other

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 melting and boiling points
  • This is due to the strong electrostatic forces of attraction between 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	Electrical conductivity	Thermal conductivity
Melting / boiling point	Strength	Strength-to-weight ratio
Density	Toxicity	Corrosion resistance
Reactivity	Lustre	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 it is strong and resistant to corrosion