Metallic bonding: delocalised electrons hold a giant metal structure together
Definition
Lattice
A regular, repeating arrangement of particles in a solid structure.
- Metals are made of giant structures that contain a very large number of metal atoms.
- The atoms sit in a regular, repeating pattern that extends throughout the solid.
- This ordered three-dimensional arrangement of particles is called a lattice.
- The pattern continues in every direction, so a metal contains no separate molecules.
Note
- Giant means a continuous structure of many bonded particles, not one unusually large atom.
- The same lattice idea is used for ionic and covalent giant structures too.
Delocalised electrons: outer-shell electrons move through the whole structure
Definition
Outer shell
The highest occupied electron shell of an atom, containing the electrons involved when the atom forms an ion.
- Every metal atom has one or more electrons in its outer shell.
- When the atoms pack together, these outer-shell electrons become delocalised.
- A delocalised electron is no longer held by any single atom or ion.
- The delocalised electrons are free to move throughout the whole giant structure.
- Losing its outer electrons leaves each atom as a positive metal ion.
- The charge matches the number of electrons released, so sodium forms Na+\text{Na}^+Na+ and magnesium forms Mg2+\text{Mg}^{2+}Mg2+.
Common Mistake
- Do not describe the electrons as fixed between pairs of atoms, because that describes covalent bonding.
- Do not attach each electron to one ion, because delocalised electrons move through the whole structure.
Metallic bonds: opposite charges attract strongly throughout the metal
Definition
Metal ion
A positively charged particle formed when a metal atom loses one or more electrons.
- Metallic bonding is the strong electrostatic attraction between the positive metal ions and the delocalised electrons.
- The delocalised electrons are shared across the whole structure rather than between a single pair of atoms.
- Each positive metal ion is attracted to the negatively charged electrons that surround it.
- These attractions act in all directions throughout the giant lattice.
- The result is a set of very strong metallic bonds holding the structure together.
Key Idea
- Positive metal ions form the regular lattice.
- Delocalised electrons move through the spaces between them.
- The strong attraction between these opposite charges is the metallic bond.
Drawing the model: positive ions surrounded by a sea of delocalised electrons
- Draw the positive metal ions as equal-sized circles arranged in neat rows.
- Put a plus sign inside each circle to show that every ion carries a positive charge.
- Add the delocalised electrons as small dots or crosses in the gaps between the ions.
- Spread these marks evenly to show the electrons are shared across the whole structure.
- Label the circles as positive metal ions and the dots or crosses as delocalised electrons.
Self review
- What type of structure do metals form?
- What does it mean to say the outer-shell electrons are delocalised?
- Why are the atoms represented as positive metal ions?
- What is a metallic bond?
- How should the delocalised electrons be shown in a metallic-bonding diagram?
