OxfordAQA International A Level Chemistry
OxfordAQA International A Level Chemistry 3.1.3 Bonding Exam Questions
Free OxfordAQA International A Level Chemistry revision for 3.1.3 Bonding: what you need to know, common mistakes and exam-style questions with answers. Covers ionic, covalent, dative and metallic bonding, crystal structures, shapes of molecules, polarity and intermolecular forces.
Practise 3.1.3 Bonding with past papers
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About OxfordAQA International A Level Chemistry 3.1.3 Bonding
Bonding is a Unit 1 topic that explains the properties of substances from their structures. You need to describe ionic, covalent, dative covalent and metallic bonding, and the four crystal types (ionic, metallic, macromolecular and molecular) with examples such as diamond, graphite, ice, iodine, magnesium and sodium chloride. You must predict shapes and bond angles for molecules and ions with up to six electron pairs using electron pair repulsion, and explain polarity and intermolecular forces. This topic links to periodicity, Group 7, organic chemistry and transition metal complexes. Examiners frequently ask for shapes with bond angles and explanations of boiling points.
What you need to know
- Ionic bonding Ionic bonding is the electrostatic attraction between oppositely charged ions in a lattice. You need formulae of compound ions such as sulfate, hydroxide, nitrate, carbonate and ammonium.
- Covalent and dative bonding A covalent bond is a shared pair of electrons. In a dative covalent (co-ordinate) bond both electrons come from one atom, as in NH4+ and H3O+.
- Metallic bonding Metallic bonding is the attraction between positive metal ions and delocalised electrons. It explains conductivity and high melting points.
- Shapes of molecules Electron pairs repel to be as far apart as possible, and lone pair-lone pair repulsion is greater than lone pair-bond pair, which is greater than bond pair-bond pair. Examples: linear 180, trigonal planar 120, tetrahedral 109.5, pyramidal 107, bent 104.5, trigonal bipyramidal 90 and 120, octahedral 90 degrees.
- Electronegativity and polarity Electronegativity is the power of an atom to attract the pair of electrons in a covalent bond. Unequal sharing makes a bond polar, but a symmetrical molecule such as CO2 has no overall dipole.
- Intermolecular forces Induced dipole-dipole (van der Waals) forces exist between all molecules and increase with size. Permanent dipole-dipole forces act between polar molecules. Hydrogen bonds form between an H attached to N, O or F and a lone pair on N, O or F, explaining the high boiling point of water and why ice is less dense than water.
Common mistakes in 3.1.3 Bonding
- Saying covalent bonds break when a simple molecular substance boils. Only the intermolecular forces are overcome.
- Giving the shape without counting lone pairs. Count all electron pairs around the central atom first, then name the shape from bonding pairs only.
- Drawing a hydrogen bond without a lone pair. The hydrogen bond goes from the delta positive H to a lone pair on N, O or F.
- Saying graphite conducts because of free ions. It conducts because each carbon has one delocalised electron.
Try three 3.1.3 Bonding exam-style questions
1. State the shape of and the bond angle in NH3. Explain the bond angle. (3 marks)
Show the mark scheme answer
Pyramidal; 107 degrees; three bonding pairs and one lone pair, and the lone pair repels more than bonding pairs, so the angle is less than 109.5.
2. Explain why the boiling point of water is much higher than that of hydrogen sulfide. (3 marks)
Show the mark scheme answer
Water forms hydrogen bonds between molecules; hydrogen sulfide has only weaker permanent dipole and van der Waals forces; more energy is needed to overcome hydrogen bonds.
3. Explain why magnesium has a higher melting point than sodium. (2 marks)
Show the mark scheme answer
Mg2+ has a higher charge and is smaller than Na+, and magnesium has more delocalised electrons per ion; so the metallic bonding (attraction) is stronger.
3.1.3 Bonding FAQs
What does OxfordAQA International A Level Chemistry 3.1.3 Bonding cover?
It covers ionic, covalent, dative and metallic bonding, crystal structures, shapes of molecules, polarity and intermolecular forces.
Which unit is 3.1.3 Bonding examined in?
It is examined in Unit 1, the first International AS paper, which covers inorganic and physical chemistry. The Unit 5 practical and synoptic paper at A2 can also assess it.
How many shapes do I need to know?
You need shapes and bond angles for molecules and ions with up to six electron pairs around the central atom, including those with lone pairs. Learn the basic shapes, then reduce the angle by about 2.5 degrees per lone pair for tetrahedral-based shapes.
