1. Structure and bonding
page 2

Interactive graphic of metallic bonding
Picture 1.1 Metal ions are held together by metallic bonds. These are created when at least one electron from each atom becomes delocalised forming a cloud of electrons.
Metallic bonds
All metals are made up of a vast collection of ions that are held together by metallic bonds. A metal atom has a positive nucleus with negative electrons outside of it. In a solid, each atom loses the outermost electron, which takes part in bonding. They form a lattice of regularly spaced positive ions. Each ion has no control over its bonding electron.
A cloud of electrons
The outermost, bonding electrons are no longer bound to individual atoms. They are spread randomly through the lattice. They form a ‘cloud’ of electrons which are free to move through the solid. The electrons behave like a gas that is confined by the edges of the piece of metal.

The bonding electrons no longer belong to any particular metal atom. They are spread out throughout the lattice. We say that they are delocalised because they are not restricted to one part of the metal lattice.

Each positive metal ion is attracted to the negatively charged delocalised electrons. The negative electrons are in turn attracted towards the positive metal ions. It is these attractions that hold the structure together forming metallic bonds.

An analogy which may help you think about this arrangement is to imagine a series of peas embedded in a ball of candy floss. The peas represent the positive metal ions and the candy floss represents the cloud of delocalised electrons.

Interactive graphic of sliding layers
Interactive graphic of sliding layers
Picture 1.2 Layers of ions can slip over each other, making a metal malleable and ductile.
Why some metals are malleable and some are ductile
Metals are malleable. This means that they can be hammered or pressed into different shapes without breaking. They are also ductile, which means that they can be drawn out into thin wires without breaking.

In each case, we are changing the shape of the metal without cracking or breaking it. This is possible because the metallic bonds are strong but not directed between particular ions.

If we bend a piece a metal, layers of metal ions can slide over one another. This process is called slip. The metal ions that have moved can reform attractions with delocalised electrons in their new positions. The shape of the metal has changed but the metallic bonds are still present and the material does not break.

On page 6, we will see how dislocations increase malleability and ductility.

Question 1-1.
a) What do we call electrons that make up the metallic bond and are free to move through a metal lattice?

b) What are the two features that make up metallic bonds?

c) A malleable material is one that can be hammered into a different shape without breaking. What name do we give to a material that breaks when it is hammered?

Summary                   Close
  • the atoms in a metal lose their outer electrons, forming
  • the ions are surrounded by a cloud of free, delocalised, electrons
  • metals are malleable and ductile because of their bonds