Chemistry SL
Structure 2: models of bonding and structure — Structure 2
- 1.
Explain, in terms of electron transfer, how an ionic bond forms between a sodium atom and a chlorine atom.
[4 marks] · no calculator - 2.
Marking analysis: A learner attempts the following task: “Explain, in terms of electron transfer, how an ionic bond forms between a sodium atom and a chlorine atom.” Their response addresses only this point: “States that the sodium atom transfers (loses) one electron from its outer shell to the chlorine atom.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 3.
Explain, in terms of shared electron pairs, how a covalent bond forms between two chlorine atoms in a Cl₂ molecule.
[3 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Explain, in terms of shared electron pairs, how a covalent bond forms between two chlorine atoms in a Cl₂ molecule.” Their response addresses only this point: “States that each chlorine atom has 7 electrons in its outer shell and needs 1 more to achieve a stable, full outer shell.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 5.
Use VSEPR theory to predict the shape and bond angle of a methane molecule, CH₄.
[3 marks] · no calculator - 6.
Marking analysis: A learner attempts the following task: “Use VSEPR theory to predict the shape and bond angle of a methane molecule, CH₄.” Their response addresses only this point: “States that the central carbon atom has 4 bonding electron pairs and no lone pairs.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 7.
Explain why metals are good conductors of electricity, in terms of their bonding and structure.
[3 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Explain why metals are good conductors of electricity, in terms of their bonding and structure.” Their response addresses only this point: “States that metallic bonding consists of a lattice of positive metal ions surrounded by a 'sea' of delocalised electrons.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 9.
Explain why giant covalent structures, such as diamond, have very high melting points.
[3 marks] · no calculator - 10.
Marking analysis: A learner attempts the following task: “Explain why giant covalent structures, such as diamond, have very high melting points.” Their response addresses only this point: “States that in a giant covalent structure, every atom is joined to neighbouring atoms by strong covalent bonds throughout the entire structure.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 11.
Explain why simple molecular substances, such as iodine, have low melting and boiling points compared to giant ionic or covalent structures.
[3 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Explain why simple molecular substances, such as iodine, have low melting and boiling points compared to giant ionic or covalent structures.” Their response addresses only this point: “States that within each molecule, the atoms are held together by strong covalent bonds.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 13.
Explain why sodium chloride conducts electricity when molten but not when solid.
[4 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “Explain why sodium chloride conducts electricity when molten but not when solid.” Their response addresses only this point: “States that sodium chloride contains charged ions.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 15.
Use VSEPR theory to predict the shape of an ammonia molecule, NH₃, and explain why its bond angle (107°) is slightly smaller than the tetrahedral angle.
[4 marks] · no calculator - 16.
Marking analysis: A learner attempts the following task: “Use VSEPR theory to predict the shape of an ammonia molecule, NH₃, and explain why its bond angle (107°) is slightly smaller than the tetrahedral angle.” Their response addresses only this point: “States that the central nitrogen atom has 3 bonding electron pairs and 1 lone pair.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 17.
Distinguish between a polar covalent bond and a non-polar covalent bond, referring to electronegativity.
[2 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “Distinguish between a polar covalent bond and a non-polar covalent bond, referring to electronegativity.” Their response addresses only this point: “States that a non-polar covalent bond forms between atoms of equal or very similar electronegativity, so shared electrons are distributed evenly.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[2 marks] · no calculator - 19.
Explain why the boiling point of water is anomalously high compared to other hydrides of Group 16 elements (e.g. H₂S), in terms of hydrogen bonding.
[3 marks] · no calculator - 20.
Marking analysis: A learner attempts the following task: “Explain why the boiling point of water is anomalously high compared to other hydrides of Group 16 elements (e.g. H₂S), in terms of hydrogen bonding.” Their response addresses only this point: “States that water molecules can form hydrogen bonds, a relatively strong intermolecular force, due to the highly electronegative oxygen bonded directly to hydrogen.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 21.
Use VSEPR theory to predict the shape and bond angle of a water molecule, H₂O, explaining why its bond angle (104.5°) is smaller than that of ammonia (107°).
[4 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Use VSEPR theory to predict the shape and bond angle of a water molecule, H₂O, explaining why its bond angle (104.5°) is smaller than that of ammonia (107°).” Their response addresses only this point: “States that the central oxygen atom has 2 bonding electron pairs and 2 lone pairs.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 23.
Explain, in terms of structure and bonding, why metals are malleable (can be hammered into shape) without shattering.
[3 marks] · no calculator - 24.
Marking analysis: A learner attempts the following task: “Explain, in terms of structure and bonding, why metals are malleable (can be hammered into shape) without shattering.” Their response addresses only this point: “States that metals consist of layers of positive metal ions arranged in a regular structure.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 25.
Sodium chloride forms a giant ionic lattice. Describe this structure, and explain why ionic compounds generally have high melting points.
[3 marks] · no calculator - 26.
Marking analysis: A learner attempts the following task: “Sodium chloride forms a giant ionic lattice. Describe this structure, and explain why ionic compounds generally have high melting points.” Their response addresses only this point: “States that positive and negative ions are arranged in a regular, repeating (alternating) pattern extending in all directions.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 27.
Explain why the boiling points of the halogens (F₂, Cl₂, Br₂, I₂) increase down the group, in terms of van der Waals (London dispersion) forces.
[3 marks] · no calculator - 28.
Marking analysis: A learner attempts the following task: “Explain why the boiling points of the halogens (F₂, Cl₂, Br₂, I₂) increase down the group, in terms of van der Waals (London dispersion) forces.” Their response addresses only this point: “States that halogen molecules are held together in the solid/liquid state only by van der Waals (London dispersion) forces between molecules.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 29.
Explain, using the formation of the ammonium ion NH₄⁺ from ammonia and a hydrogen ion, what is meant by a dative (coordinate) covalent bond.
[3 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “Explain, using the formation of the ammonium ion NH₄⁺ from ammonia and a hydrogen ion, what is meant by a dative (coordinate) covalent bond.” Their response addresses only this point: “States that a dative covalent bond forms when one atom provides both electrons of the shared pair, rather than one electron from each atom.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator