How does the bonding and structure of a material explain its properties?
Bonding and properties: covalent bonding (molecular and network), ionic bonding, and how each structure explains melting point, conductivity and solubility.
An SQA National 5 Chemistry answer on bonding and properties, covering covalent molecular, covalent network and ionic substances, how each forms, and how the structure explains melting point, electrical conductivity and solubility.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this key area is asking
The SQA wants you to describe how covalent and ionic bonds form, recognise the three main structures (covalent molecular, covalent network and ionic), and explain a substance's melting point, electrical conductivity and solubility from its bonding and structure. The marks come from linking a property back to the structure with precise wording, not from listing properties on their own.
The two kinds of bond
A quick guide to which one you have: a compound of a metal and a non-metal is usually ionic; a compound of non-metals only is usually covalent.
Covalent molecular substances
Covalent network substances
Ionic compounds
Worked example: identifying a structure from data
Examples in context
The contrast between graphite and diamond explains everyday choices: graphite is used in pencil leads and as an electrode because its free electrons conduct and its layers slide, while diamond is used in cutting tools because its rigid covalent network is extremely hard. Road salt and table salt are ionic, which is why salt water conducts and pure dry salt does not. The fact that sugar (covalent molecular) melts and caramelises gently in a pan, while salt (ionic) needs a furnace to melt, is the low-melting-point property of molecular substances in action.
Try this
Q1. State what is meant by a covalent bond. [1 mark]
- Cue. A shared pair of electrons between two non-metal atoms.
Q2. Explain why an ionic compound conducts electricity when dissolved in water but not when solid. [2 marks]
- Cue. Conduction needs free-moving charged particles; dissolving frees the ions, but in the solid they are locked in the lattice.
Q3. Explain why diamond has a much higher melting point than iodine, which is covalent molecular. [2 marks]
- Cue. Diamond is a covalent network needing many strong bonds broken; iodine needs only weak forces between molecules overcome.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 2019 style3 marksSodium chloride has a melting point of 801 degrees C and conducts electricity when molten or dissolved in water, but not when solid. Explain these properties in terms of its bonding and structure.Show worked answer →
Markers reward the lattice idea, the explanation of the high melting point, and the explanation of conduction.
Sodium chloride is an ionic compound made of a giant lattice of positive sodium ions and negative chloride ions held together by strong electrostatic forces of attraction between the oppositely charged ions.
A large amount of energy is needed to overcome these strong forces throughout the lattice, so the melting point is very high.
It conducts only when molten or dissolved because conduction needs charged particles that are free to move. In the solid the ions are locked in fixed positions, but when melted or dissolved the ions are free to move and carry charge.
SQA N5 2021 style3 marksDiamond and carbon dioxide are both made only of covalently bonded atoms, yet diamond has a very high melting point and carbon dioxide is a gas at room temperature. Explain the difference in terms of structure.Show worked answer →
A 3 mark answer needs the network structure of diamond, the molecular structure of carbon dioxide, and the contrast in what must be overcome.
Diamond is a covalent network: every carbon atom is joined to others by strong covalent bonds in one giant, continuous structure. To melt it, a huge number of strong covalent bonds must be broken throughout the network, so its melting point is extremely high.
Carbon dioxide is covalent molecular: it is made of small, separate molecules. The covalent bonds inside each molecule are strong, but the forces between the molecules are weak. Only these weak forces between molecules need to be overcome to melt or boil it, so it is a gas at room temperature.
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Sources & how we know this
- SQA National 5 Chemistry Course Specification — SQA (2019)