The nature of the particles involved depends on the type of bonding and…

The idea

The particles that make up a substance are not always the same kind. In a simple molecular substance such as water, the particles are molecules held together by weak intermolecular forces. In a giant ionic structure such as sodium chloride, the particles are ions held in a lattice by strong electrostatic forces. In a giant covalent structure such as diamond, the particles are atoms joined by strong covalent bonds throughout the structure. In a metal such as copper, the particles are positive ions in a sea of delocalised electrons. So the type of bonding and the structure determine what the particles are and how strongly they interact, which in turn affects melting and boiling points and other physical properties.

What earns the marks

• States that the particles in a substance may be atoms, ions or molecules depending on the type of bonding present.
• Links simple molecular structures to molecules held together by weak intermolecular forces.
• Links giant ionic structures to ions held in a lattice by strong electrostatic forces.
• Links giant covalent structures to atoms joined by strong covalent bonds throughout the structure.
• Links metals to positive ions in a sea of delocalised electrons.
• Explains that the type of bonding and structure affects the strength of forces between particles and therefore physical properties such as melting and boiling points.

Common mistakes and how to put them right

• Saying that all substances contain molecules.

  Put it right by stating that giant ionic, giant covalent and metallic structures contain ions or atoms rather than molecules.

• Saying that intermolecular forces are covalent bonds.

  Put it right by stating that intermolecular forces act between molecules, while covalent bonds act within molecules.

• Saying that metals contain neutral atoms only.

  Put it right by stating that metals contain positive ions and delocalised electrons.

Exam tips

• Identify the type of bonding and structure first, then name the particles and the forces between them.
• Use the correct particle term for each structure: molecules for simple molecular, ions for ionic, atoms for giant covalent, and positive ions with delocalised electrons for metals.
• Link the particle type and force strength to a physical property such as melting point to show full understanding.