Properties of metals and alloys — AQA GCSE Chemistry
Test yourself on Properties of metals and alloys with AQA GCSE practice questions.
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Properties of metals and alloys explained
Melting and boiling require energy to overcome the forces holding particles together.
Read the full explanation
In a metal, the particles are positive ions held by strong metallic bonds to a sea of delocalised electrons. Because these bonds act throughout a giant lattice, a large amount of energy is needed to break them. This is why most metals have high melting and boiling points. For example, magnesium melts at about 650 °C and iron at about 1538 °C, both much higher than the melting point of a simple molecular substance such as iodine. The stronger the metallic bonding and the more electrons donated per atom, the higher the melting point tends to be. Metals with weaker metallic bonding, such as mercury, are liquid at room temperature.
Your focus
- Explain why most metals have high melting and boiling points in terms of strong metallic bonding.
- Use data to compare the melting points of metals with those of simple molecular substances.
- Describe how the strength of metallic bonding varies between different metals.
Properties of metals and alloys exam tips
Marking Points
- Melting and boiling involve overcoming the strong metallic bonds between positive metal ions and delocalised electrons.
- The giant lattice means many strong bonds must be broken, so a large amount of energy is required.
- Most metals therefore have high melting and boiling points compared with simple molecular substances.
- The strength of metallic bonding varies between metals, so melting points vary; for example, mercury is liquid at room temperature while iron has a very high melting point.
- A valid comparison, such as magnesium melting at about 650 °C versus iodine melting at about 114 °C, supports the explanation.
Examiner Tips
- 💡Always name the force being overcome when explaining a melting or boiling point.
- 💡Use a comparison with a simple molecular substance to make the high value meaningful.
- 💡If a data table is given, quote a specific melting point to support your explanation rather than saying it is high.
Common Mistakes
- Saying that melting breaks covalent bonds inside metal molecules; the correction is that metallic bonds between ions and delocalised electrons are overcome.
- Claiming that all metals have equally high melting points; the correction is that the strength of metallic bonding differs, so values range widely.
- Stating that melting point depends on the number of delocalised electrons only; the correction is that ion charge, ion size and lattice arrangement also affect bond strength.