Bonding, structure, and the properties of matter — GCSE Chemistry Revision
Everything you need to revise bonding, structure, and the properties of matter for GCSE Chemistry: clear notes, the key facts and terms to learn, the mistakes that cost students marks, and practice questions with answers.
Revision notes
Types of Chemical Bonds
Chemical bonds form when atoms achieve a stable electron arrangement, typically a full outer shell. The three main types are ionic, covalent, and metallic. Ionic bonds involve the transfer of electrons between a metal and a non-metal, forming oppositely charged ions that are attracted to each other. Covalent bonds involve the sharing of electrons between two non-metal atoms. Metallic bonds involve a 'sea' of delocalised electrons shared among positive metal ions. Each bond type gives rise to distinct properties.
Ionic Bonding and Structures
Ionic bonds form between a metal (electron donor, forms positive ion) and a non-metal (electron acceptor, forms negative ion). The electrostatic attraction between these oppositely charged ions creates a strong ionic bond. These bonds result in giant ionic lattice structures. In an ionic lattice, each ion is surrounded by oppositely charged ions in a regular, repeating pattern. This strong attraction explains their high melting/boiling points and electrical conductivity when molten or dissolved.
Covalent Bonding and Structures
Covalent bonds occur when non-metal atoms share pairs of electrons to achieve stable outer shells. These can form simple molecular structures (e.g., H₂O, CO₂) or giant covalent structures (e.g., diamond, silicon dioxide). Simple molecular substances have weak intermolecular forces, leading to low melting/boiling points. Giant covalent structures, however, have strong covalent bonds throughout the entire lattice, resulting in very high melting/boiling points and hardness.
Metallic Bonding and Properties
Metallic bonding occurs in metals. Metal atoms lose their outer shell electrons, becoming positive metal ions. These delocalised electrons are free to move throughout the structure, forming a 'sea' of electrons that attracts the positive metal ions. This strong electrostatic attraction holds the lattice together. This model explains key metal properties: good electrical and thermal conductivity (due to delocalised electrons), malleability, and ductility (layers of ions can slide).
Key facts
- Ionic bonds form between metals and non-metals by electron transfer.|Covalent bonds form between non-metals by electron sharing.|Metallic bonds involve a 'sea' of delocalised electrons and positive metal ions.|Giant ionic lattices have high melting points and conduct electricity when molten or dissolved.|Simple molecular structures have low melting points due to weak intermolecular forces.|Giant covalent structures (e.g., diamond) have very high melting points due to strong covalent bonds.
Key terms
- Ionic Bond::A strong electrostatic force of attraction between oppositely charged ions formed by the transfer of electrons from a metal to a non-metal.|Covalent Bond::A strong bond formed when two non-metal atoms share one or more pairs of electrons to achieve a full outer shell.|Metallic Bond::The strong electrostatic attraction between the positive metal ions and the delocalised 'sea' of electrons in a metallic lattice.|Delocalised Electrons::Electrons in a metallic structure that are not associated with a single atom or bond, but are free to move throughout the entire structure.|Intermolecular Forces::Weak forces of attraction between simple discrete molecules, not within the molecules themselves.|Giant Covalent Structure::A large structure where all atoms are held together by strong covalent bonds in a continuous lattice (e.g., diamond, graphite).
Common mistakes
- Confusing intermolecular forces with covalent bonds in simple molecular structures.|Thinking that ionic compounds conduct electricity as solids.|Describing metallic bonding as ions losing and gaining electrons.|Assuming all covalent substances have low melting points (forgetting giant covalent structures).
Exam tips
- Always specify 'molten or dissolved' when discussing ionic conductivity.|Draw dot-and-cross diagrams carefully, showing only outer electrons.|When explaining properties, link the bond type/structure directly to the property (e.g., 'strong electrostatic forces require lots of energy to overcome').|Remember to mention 'delocalised' electrons for metallic bonding explanations.
Quick quiz
1. Which statement best describes an ionic bond?
- A bond where electrons are shared between two non-metal atoms.
- A bond between metal ions and a 'sea' of delocalised electrons.
- A bond formed by the transfer of electrons from a metal atom to a non-metal atom.
- A weak force of attraction between simple molecules.
Show answer
A bond formed by the transfer of electrons from a metal atom to a non-metal atom. — An ionic bond involves the transfer of electrons, typically from a metal to a non-metal, forming oppositely charged ions that are electrostatically attracted.
2. Which property is characteristic of a substance with a giant ionic lattice structure?
- Low melting point.
- Good electrical conductivity as a solid.
- Soluble in non-polar solvents.
- High melting point.
Show answer
High melting point. — Giant ionic lattices have strong electrostatic forces between ions, requiring a large amount of energy to overcome, leading to high melting points.
3. What allows metals to conduct electricity?
- Their fixed positions in a lattice.
- The presence of positive metal ions.
- The movement of delocalised electrons.
- Strong covalent bonds between atoms.
Show answer
The movement of delocalised electrons. — The 'sea' of delocalised electrons in metals are free to move and carry charge, enabling electrical conductivity.
4. Why do simple molecular substances have low melting points?
- They have weak covalent bonds.
- They have strong intermolecular forces.
- They have weak forces of attraction between molecules.
- They are made of single atoms.
Show answer
They have weak forces of attraction between molecules. — Simple molecular substances have strong covalent bonds within molecules, but only weak intermolecular forces between molecules, which require little energy to overcome.
5. Which of these substances is an example of a giant covalent structure?
- Sodium chloride (NaCl)
- Water (H₂O)
- Diamond (C)
- Magnesium (Mg)
Show answer
Diamond (C) — Diamond is a giant covalent structure where carbon atoms are covalently bonded in a continuous lattice. Sodium chloride is ionic, water is simple molecular, and magnesium is metallic.
Exam-style questions
Describe the bonding in sodium chloride (NaCl) and explain why it has a high melting point. (4 marks) [4 marks]
Show mark scheme
- Sodium is a metal and chlorine is a non-metal, so they form an ionic bond.
- Electrons are transferred from sodium atoms to chlorine atoms, forming Na+ and Cl- ions.
- There are strong electrostatic forces of attraction between these oppositely charged ions.
- These forces require a large amount of energy to overcome, resulting in a high melting point.
Explain why solid metals are good electrical conductors. (3 marks) [3 marks]
Show mark scheme
- Metals have a 'sea' of delocalised electrons.
- These electrons are free to move throughout the metallic structure.
- They can carry charge / flow when a potential difference is applied.
Explain why iodine (I₂) has a low melting point, whereas diamond has a very high melting point. (4 marks) [4 marks]
Show mark scheme
- Iodine is a simple molecular structure with strong covalent bonds within each molecule.
- However, there are only weak intermolecular forces between the iodine molecules.
- Little energy is required to overcome these weak intermolecular forces, so it has a low melting point.
- Diamond is a giant covalent structure with strong covalent bonds extending throughout the entire lattice, requiring a lot of energy to break, hence a very high melting point.
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