Bonding and structureEdexcel A-Level Chemistry: Topic test

20 questions, 54 marks

Edexcel A-Level Chemistry

Bonding and structure topic test

Total 54 marks

Name

Class

Date

1
Lithium fluoride, LiF, and potassium iodide, KI, are both white ionic solids with the same type of lattice.
(a)
Which observation provides evidence that potassium iodide contains ions?
[1 mark]
AIt dissolves in water to give a neutral solution
BIt has a high melting temperature
CIt conducts electricity when molten but not when solid
DIt is brittle and shatters when struck
(b)
How many electrons are shown in the outer shell of a K⁺ ion in a dot-and-cross diagram?
[1 mark]
A0
B1
C2
D8
(c)
Explain why lithium fluoride has a higher melting temperature than potassium iodide.
[2 marks]
Total for question 1: 4 marks
2
In aqueous acid, a hydrogen ion does not exist on its own. It bonds to a water molecule to form the oxonium ion, H₃O⁺.
(a)
Which describes the bond formed between a hydrogen ion and the oxygen atom of a water molecule?
[1 mark]
AAn ionic bond between H⁺ and O²⁻
BA dative covalent bond, with both electrons provided by the oxygen atom
CA covalent bond, with one electron provided by each atom
DA hydrogen bond between H⁺ and the lone pair on oxygen
(b)
What is the shape of the oxonium ion, H₃O⁺?
[1 mark]
ATrigonal pyramidal
BTrigonal planar
CTetrahedral
DBent
(c)
State what is meant by electronegativity. Explain why the O–H bonds in the oxonium ion are polar.
[2 marks]
Total for question 2: 4 marks
3
Trichloromethane, CHCl₃, boils at 61 °C and tetrachloromethane, CCl₄, boils at 77 °C. The Pauling electronegativity values are: H 2.1, C 2.5 and Cl 3.0.
(a)
Explain why tetrachloromethane is a non-polar molecule although it contains polar bonds, whereas trichloromethane is a polar molecule.
[3 marks]
(b)
Explain why tetrachloromethane has a higher boiling temperature than trichloromethane, even though trichloromethane molecules are polar.
[4 marks]
Total for question 3: 7 marks
4
Dry ice (solid carbon dioxide) turns directly into a gas at −78 °C. Silicon(IV) oxide melts at 1710 °C, sodium at 98 °C and calcium fluoride at 1418 °C.
(a)
Explain the differences in the melting temperatures of dry ice, sodium, calcium fluoride and silicon(IV) oxide in terms of structure and bonding.
[6 marks]
(b)
Predict, with reasons, which of the four substances conduct electricity as solids and which conduct when molten. Explain how the behaviour of calcium fluoride is evidence for the existence of ions.
[6 marks]
Total for question 4: 12 marks
5
A chemist is studying the shapes of the carbonate ion, CO₃²⁻, found in limestone, and the sulfate ion, SO₄²⁻, found in gypsum.
(a)
What is the shape of the carbonate ion, CO₃²⁻, and the O–C–O bond angle?
[1 mark]
ATetrahedral, 109.5°
BTrigonal pyramidal, 107°
CTrigonal planar, 120°
DLinear, 180°
(b)
Which statement explains the shape of the sulfate ion, SO₄²⁻?
[1 mark]
AThe four oxygen atoms attract one another
BA lone pair on sulfur pushes the oxygen atoms into a pyramid
CRepulsion between the three double bonds and the single bond forces them into a plane
DThe four regions of electron density around sulfur repel one another as far apart as possible, giving 109.5°
(c)
The sulfite ion, SO₃²⁻, has three oxygen atoms bonded to a central sulfur atom, which also has one lone pair. Deduce the shape of the sulfite ion and explain why its bond angle is less than 109.5°.
[2 marks]
Total for question 5: 4 marks
6
Ethanol, C₂H₅OH, and methoxymethane, CH₃OCH₃, are isomers with the molecular formula C₂H₆O. Ethanol boils at 78 °C and methoxymethane boils at −24 °C.
(a)
Which describes the shape of the bonds around the oxygen atom in ethanol?
[1 mark]
ALinear
BBent (V-shaped)
CTrigonal planar
DTetrahedral
(b)
Why is ethanol completely miscible with water?
[1 mark]
AEthanol molecules can form hydrogen bonds with water molecules
BEthanol is an ionic compound that is hydrated by water
CEthanol has stronger London forces than water
DEthanol reacts with water to form a new compound
(c)
Explain, in terms of intermolecular forces, why ethanol has a much higher boiling temperature than methoxymethane.
[2 marks]
Total for question 6: 4 marks
7
Some data for carbon–halogen bonds are: C–F, bond length 0.138 nm and mean bond enthalpy 467 kJ mol⁻¹; C–Cl, 0.177 nm and 346 kJ mol⁻¹; C–I, 0.214 nm and 228 kJ mol⁻¹. The Pauling electronegativity values are: C 2.5, F 4.0 and Cl 3.0.
(a)
Explain the trend in the strength of the carbon–halogen bonds from C–F to C–I.
[3 marks]
(b)
State what is meant by electronegativity. Explain why the C–F bond is polar and why tetrafluoromethane, CF₄, is a non-polar molecule.
[4 marks]
Total for question 7: 7 marks
8
Ammonia, NH₃, boils at −33 °C and phosphine, PH₃, boils at −88 °C. Hydrogen fluoride, HF, boils at 20 °C. Boron trifluoride, BF₃, is a gas at room temperature. The Pauling electronegativity values are: H 2.1, B 2.0, N 3.0, P 2.1 and F 4.0.
(a)
Explain why ammonia has a higher boiling temperature than phosphine, and why hydrogen fluoride has a higher boiling temperature than ammonia.
[6 marks]
(b)
Ammonia and boron trifluoride each have three bonding pairs around the central atom. Deduce the shape and bond angle of each molecule, and explain why ammonia is a polar molecule but boron trifluoride is not.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).