How do atoms join together, and how does bonding explain the properties of a substance?
Ionic, covalent and metallic bonding, how each type of bond forms, the structures they produce, and how bonding explains the properties of ionic compounds, simple molecules, giant covalent structures and metals.
A focused answer to Edexcel GCSE Combined Science Topic 1 (CC1), covering ionic, covalent and metallic bonding, how each type forms, the structures they produce, and how bonding explains the properties of ionic compounds, simple molecules, giant covalent structures and metals.
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What this dot point is asking
Edexcel wants you to describe ionic, covalent and metallic bonding, explain how each forms in terms of electrons, describe the structures produced, and explain how the bonding and structure give rise to the properties of ionic compounds, simple molecules, giant covalent structures and metals.
Ionic bonding
Ionic compounds (such as sodium chloride) have high melting and boiling points because a lot of energy is needed to overcome the many strong forces. They conduct electricity only when molten or dissolved, because then the ions are free to move; in the solid the ions are fixed.
Covalent bonding
Simple molecular substances have low melting and boiling points because the forces between the molecules (intermolecular forces) are weak and easily overcome, even though the covalent bonds inside each molecule are strong. They usually do not conduct electricity.
Giant covalent structures (diamond, graphite, silicon dioxide) have very high melting points because every atom is joined by strong covalent bonds. Diamond is very hard; graphite is soft and conducts electricity because each carbon has a delocalised electron.
Metallic bonding
This explains metal properties: the delocalised electrons carry charge, so metals conduct electricity and heat; the layers of ions slide over each other, so metals are malleable (can be bent and shaped); and the strong metallic bonds give high melting points.
The big idea running through all of this is that structure and bonding decide properties. If you are told a substance conducts only when molten, has a high melting point and dissolves in water, you can deduce it is ionic. If it is a gas or a runny liquid that does not conduct, it is a simple molecular substance. If it conducts as a solid and can be bent, it is a metal. Being able to reason in both directions, from bonding to properties and from properties back to bonding, is the single most useful skill in this topic.
Try this
Q1. State the type of bonding between a metal and a non-metal. [1 mark]
- Cue. Ionic bonding.
Q2. Explain why metals conduct electricity. [2 marks]
- Cue. They have delocalised (free) electrons that can move through the structure and carry charge.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20204 marksExplain why sodium chloride has a high melting point and only conducts electricity when molten or dissolved in water.Show worked answer →
A 4-mark explain question linking ionic bonding to properties.
Sodium chloride has a giant ionic lattice held together by strong electrostatic forces of attraction between oppositely charged ions (1 mark). A lot of energy is needed to overcome these strong forces, so it has a high melting point (1 mark). When solid, the ions are held in fixed positions and cannot move, so it does not conduct (1 mark). When molten or dissolved, the ions are free to move and carry charge, so it conducts electricity (1 mark).
Markers reward strong electrostatic forces for the high melting point, and free-moving ions for conduction only when molten or in solution.
Edexcel 20223 marksExplain why metals are good conductors of electricity and can be bent into shape (are malleable).Show worked answer →
A 3-mark explain question on metallic bonding.
Metals have a giant structure of positive ions surrounded by a sea of delocalised (free) electrons (1 mark). The delocalised electrons are free to move through the structure and carry charge, so metals conduct electricity (1 mark). The layers of ions can slide over each other without breaking the metallic bonds, so metals can be bent and shaped (they are malleable) (1 mark).
Markers reward delocalised electrons carrying charge for conduction, and layers of ions sliding for malleability.
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Sources & how we know this
- Edexcel GCSE (9-1) Combined Science (1SC0) specification — Pearson (2016)