Chemical Bonding (Ionic, Covalent and Metallic): Chemistry 0620 (Cambridge O Level / IGCSE)
Syllabus 2.4, 2.5, 2.6, 2.7 · Strand 2 Atoms, elements and compounds
- Questions
- 10
- Total marks
- 50
- Tier mix
- 2 Core · 8 Extended
0 of 10 questions completed
Syllabus coverage
- 2.4 4 questions completed
- 2.5 4 questions completed
- 2.6 1 question completed
- 2.7 2 questions completed
Bonding (syllabus sections 2.4–2.7) explains why substances behave the way they do, and 0620 examiners love asking you to connect structure to properties. Ionic bonds form when metal atoms transfer electrons to non-metal atoms, producing oppositely charged ions held in a giant lattice by strong electrostatic attraction, hence high melting points and electrical conductivity only when molten or dissolved.
Covalent bonds are shared pairs of electrons between non-metal atoms. You should be able to draw dot-and-cross diagrams for molecules such as H₂O, CO₂, CH₄ and N₂, and explain why simple molecular substances have low melting points (weak forces between molecules, not weak bonds). Extended candidates compare the giant covalent structures of diamond, graphite and silicon dioxide, graphite’s delocalised electrons and slippery layers are a classic six-marker, and describe metallic bonding as positive ions in a “sea” of delocalised electrons, which accounts for conductivity and malleability.
The most costly mistake is vague language: “strong bonds” without saying which forces are overcome scores nothing. The original questions below train precise explanations, each with a full worked solution.
Question 1
Lithium fluoride (LiF) crystals are used as windows in some ultraviolet spectrometers, because thin slices of the crystal let UV light pass through them. Which statement correctly describes what happens when lithium atoms and fluorine atoms react together to form lithium fluoride?
Question 2
A farm operates an anaerobic digester that breaks down animal waste to produce biogas, which is mostly methane, . The biogas is stored and transported as a gas, and only turns into a liquid if it is cooled below .
(a) State the type of bonding present between the carbon atom and the hydrogen atoms in a molecule of methane, and describe, in terms of electrons, how this bonding holds the atoms together. [3]
(b) Methane is a simple molecular substance. Describe two properties of methane that are typical of simple molecular substances, referring to its boiling point and its ability to conduct electricity. [2]
Question 3
Nigari is a coagulant used in tofu-making that is mainly magnesium chloride, , produced by evaporating seawater. A food scientist studying nigari investigates the bonding and structure of magnesium chloride.
(a) Describe, in terms of electron transfer, how magnesium and chlorine atoms react to form the ions present in magnesium chloride. [3]
(b) Describe the structure of solid magnesium chloride. [2]
(c) Explain why solid magnesium chloride does not conduct electricity, but molten magnesium chloride does conduct electricity. [2]
Question 4
A specialist workshop cuts and polishes industrial glass panels using saw blades tipped with diamond, chosen because diamond is the hardest known natural material. In the same workshop, a furnace uses crucibles made from silicon dioxide, , to melt metal alloys at very high temperatures, and the moving parts of the cutting machine are lubricated with graphite powder.
(a) Describe the structure and bonding in diamond, and use it to explain why diamond is extremely hard. [3]
(b) Silicon dioxide has a giant covalent structure in which each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms. Explain why silicon dioxide, like diamond, has a very high melting point. [2]
(c) Graphite has a different structure from diamond, even though both are forms of carbon.
(i) Describe the structure of graphite. [2]
(ii) Use the structure of graphite to explain why it is soft and slippery, and why it conducts electricity, unlike diamond. [3]
Question 5
A silversmith is raising a bowl: she starts with a flat, circular disc of silver and repeatedly strikes it with a mallet over a curved wooden former, gradually curving the flat disc into a rounded bowl shape. Even after hundreds of hammer blows, the silver does not split or crack; it just changes shape smoothly. Which statement correctly explains, in terms of structure and bonding, why the silver disc can be reshaped this way without breaking?
Question 6
Aluminium oxide is a hard, chemically stable compound that forms a thin, protective coating naturally on aluminium cooking foil and window frames, stopping the metal underneath from corroding further. Aluminium atoms (Group III) react with oxygen atoms (Group VI) to form this compound. Which statement correctly describes the ions formed and the ratio in which they combine in aluminium oxide?
Question 7
A city trials a new bus that runs on a hydrogen fuel cell. Inside the fuel cell, hydrogen gas reacts with oxygen gas from the air, and the only substance released from the exhaust pipe is water, mostly as vapour.
(a) State the type of bonding between the oxygen atom and the hydrogen atoms in a molecule of water, and describe, in terms of electrons, how this bonding holds the atoms together. [3]
(b) Water's boiling point, , is much lower than the melting point of an ionic compound such as sodium chloride, . Explain, in terms of structure and bonding, why water has such a comparatively low boiling point. [2]
(c) State whether pure water conducts electricity, and explain your answer in terms of structure and bonding. [1]
Question 8
A concert production crew uses blocks of dry ice, solid carbon dioxide (), to create a low-lying fog effect on stage. As the blocks warm up, they change directly from a solid into carbon dioxide gas.
(a) Describe, in terms of electrons, the covalent bonding between the carbon atom and each oxygen atom in a molecule of carbon dioxide, including the number of electron pairs shared in each bond. [4]
(b) State the type of structure formed by carbon dioxide molecules, and explain why carbon dioxide can change from a solid to a gas at a much lower temperature than a giant covalent structure such as silicon dioxide changes from a solid to a liquid. [3]
(c) State and explain whether carbon dioxide gas conducts electricity. [2]
Question 9
A materials science teacher sets up a "mystery substances" identification activity for her class. She gives each group data for two unlabelled solid samples, P and Q, without revealing their names:
Sample P: melting point . Does not conduct electricity as a solid, but conducts well when melted or dissolved in water. Dissolves readily in water.
Sample Q: melting point (it is a gas at room temperature). Does not conduct electricity as a solid, liquid or gas. Does not dissolve appreciably in water.
(a) State the type of structure and bonding present in sample P and in sample Q. [2]
(b) Use the structure and bonding of each sample to explain the large difference between their melting points. [3]
(c) Explain, in terms of structure and bonding, why sample P conducts electricity only when it is molten or dissolved in water, but not when it is a solid. [2]
(d) State whether you would expect sample P or sample Q to be more soluble in water, and give a reason for your answer based on structure and bonding. [2]
Question 10
An electrician upgrades the wiring in an old building, replacing aluminium cables with copper cables, because copper is an even better electrical conductor. Which statement correctly explains, in terms of structure and bonding, why a metal such as copper conducts electricity?