Metallic bonding

Metallic bonding

Lessons

In this lesson, we will learn:

  • To describe the features of metallic bonding and the structure of pure metals.
  • How to explain the properties of metals using the theory of metallic bonding.

Notes:

  • We saw earlier that ionic and covalent bonding are bonding types that hold compounds and small molecules together, but there is another type of bonding that occurs in elemental samples of metals.
  • Metallic bonding, as the name suggests, occurs in samples of metal-only atoms, including pure metallic samples, and explains the properties of pure metals that we observe.
    • Metallic bonding occurs in PURE METAL SAMPLES. It occurs in alloys too, which are 'mixtures' of different metals (more on alloys next lesson).
    • Metallic bonding does NOT occur in metal compounds with non-metal atoms. That is ionic bonding!
  • Metallic bonding gives chemical substances a structure with the following features:
    • Metallic bonding creates a lattice of positively charged ions.
    • Between these positive ions, there is a sea of negative delocalized electrons. These are the electrons that the metal atoms (that are now ions!) had lost, so they could gain a full outer shell. See the diagram below.
  • As with any theory, the theory is used to explain the observations made. Metallic bonding explains the properties of metals in the following ways:
    • There is a strong electrostatic attraction between the positive metal ions and the delocalized electrons. This force of attraction takes a lot of energy to overcome and force the positive ions apart. This explains why the majority of metals have a very high melting point.
    • The sea of delocalized electrons is fluid, which means the metal ions can move because they aren't rigidly stuck in one place in the lattice. This explains why many metals are malleable and ductile:
      • A material that is malleable can be bent and re-shaped when heated up. Heating up malleable metal and hammering/chiseling it into different shapes is how blacksmithing works!
      • A material that is ductile can be bent and drawn into thin wires. Copper is very ductile and most electrical wires are made from it.
    • The fluid sea of negatively charged delocalized electrons easily carry electric charge and heat energy throughout the lattice. This explains why metals are good conductors of both electricity and heat.
  • Metallic structure and bonding applies not only to pure substances of only one metal element, but also mixtures of different metals combined – these are called alloys which are made to obtain unique or more precise properties of two or more metal elements. Alloys will be looked at in our next lesson!
  • Introduction
    What is metallic bonding?
    a)
    How is metallic bonding different from ionic/covalent bonding?

    b)
    Features of metallic bonding.

    c)
    Explaining metal properties using theory of metallic bonding.