3.3 Metallic Bonding
By the end of this chapter, students should be able to:
- Define metallic bonding and draw an illustration to represent it.
1 What Is Metallic Bonding? ▾
In a metal, atoms are packed closely together in a regular arrangement called a lattice. Metal atoms in the lattice tend to lose their outer-shell electrons and become positive ions.
The released outer-shell electrons occupy new energy levels and are free to move throughout the whole structure. We call these delocalised electrons (mobile electrons).
Every metal lattice follows this same pattern, whatever the element. For magnesium, for example, the lattice consists of Mg2+ ions surrounded by a sea of delocalised electrons:
2 Strength & Properties of Metals ▾
The strength of metallic bonding is not fixed — it increases with:
- Increasing positive charge on the ions in the lattice
- Decreasing size of the metal ions in the lattice
- Increasing the number of mobile (delocalised) electrons per atom
High Melting & Boiling Points
Most metals have high melting and boiling points. A large amount of energy is needed to weaken the strong attractive forces between the metal ions and the delocalised electrons — these forces can only be overcome at high temperatures.
Metals Conduct Electricity
When a voltage is applied across a piece of metal, a current flows because the delocalised electrons are free to move throughout the structure.
Metals Conduct Heat
Thermal conduction is partly due to the movement of delocalised electrons, but is mainly caused by vibrations passed from one metal ion to the next through the lattice.
- Describe metallic bonding as the electrostatic attraction between positive metal ions and delocalised electrons.
- State that the attraction acts in all directions (non-directional).
- Link stronger bonding to higher ionic charge, smaller ionic radius, and more delocalised electrons per atom.
- Be able to sketch a lattice of ions surrounded by a “sea” of delocalised electrons.
- Don’t say electrons are just “free to move” without saying they are delocalised, not tied to one atom.
- Don’t forget graphite is an exception — a covalent structure that does conduct.
- Don’t say ionic solids conduct electricity — they don’t, while solid.
- Don’t describe metallic bonding as directional — unlike covalent bonding, it isn’t.
- Metallic bond = electrostatic attraction between positive metal ions and a “sea” of delocalised electrons.
- Bond strength increases with: higher ionic charge, smaller ionic radius, more delocalised electrons per atom.
- High melting/boiling points: a lot of energy is needed to overcome the strong attraction.
- Metals conduct electricity and heat: delocalised electrons carry charge; ion vibrations mainly carry heat.