BondingAQA A-Level Chemistry: Topic test

20 questions, 54 marks

AQA A-Level Chemistry

Bonding topic test

Total 54 marks

Name

Class

Date

1
Lithium carbonate, Li₂CO₃, is used in rechargeable batteries and in the manufacture of glass. It is made of lithium ions and carbonate ions, CO₃²⁻.
(a)
Which statement explains the formula Li₂CO₃?
[1 mark]
AEach lithium atom gains two electrons to form a Li²⁻ ion
BTwo Li⁺ ions are needed to balance the charge on one CO₃²⁻ ion
CLithium forms a 2+ ion and the carbonate ion has a charge of 1−
DThe carbonate ion contains two lithium atoms joined by covalent bonds
(b)
Which compound contains both ionic bonding and a dative covalent bond?
[1 mark]
ASodium chloride, NaCl
BMagnesium oxide, MgO
CHydrogen chloride, HCl
DAmmonium chloride, NH₄Cl
(c)
Explain why solid lithium carbonate does not conduct electricity but molten lithium carbonate does.
[2 marks]
Total for question 1: 4 marks
2
Phosphine, PH₃, is a toxic gas. It reacts with H⁺ ions in acid to form the phosphonium ion, PH₄⁺. A phosphorus atom has five electrons in its outer shell.
(a)
Which statement describes the bond formed between PH₃ and H⁺?
[1 mark]
AA dative covalent bond, in which both shared electrons come from the phosphorus atom
BA covalent bond, in which one electron comes from phosphorus and one from H⁺
CAn ionic bond, formed by transfer of an electron from phosphorus to H⁺
DA dative covalent bond, in which both shared electrons come from H⁺
(b)
How many bonding pairs and lone pairs of electrons are there around the phosphorus atom in PH₄⁺?
[1 mark]
A3 bonding pairs and 1 lone pair
B4 bonding pairs and 1 lone pair
C4 bonding pairs and no lone pairs
D5 bonding pairs and no lone pairs
(c)
Explain why a molecule of PH₃ is able to form a dative covalent bond with an H⁺ ion.
[2 marks]
Total for question 2: 4 marks
3
A materials scientist compares three solids at room temperature. Silicon dioxide (quartz), SiO₂, melts at 1710 °C and does not conduct electricity. Solid carbon dioxide (dry ice) sublimes at −78 °C. Copper melts at 1085 °C, conducts electricity as a solid and can be drawn into wires.
(a)
Explain why silicon dioxide has a much higher melting point than solid carbon dioxide.
[3 marks]
(b)
Explain, in terms of structure and bonding, why copper conducts electricity and can be drawn into wires.
[4 marks]
Total for question 3: 7 marks
4
Xenon forms the compound xenon tetrafluoride, XeF₄, a colourless solid that melts at 117 °C. A xenon atom has eight electrons in its outer shell, four of which are shared with fluorine atoms in XeF₄. Pauling electronegativity values: Xe 2.6 and F 4.0. The boiling points of xenon and fluorine, F₂, are −108 °C and −188 °C.
(a)
Explain the shape of the XeF₄ molecule, state the F–Xe–F bond angle, and explain why XeF₄ has no permanent dipole even though the Xe–F bonds are polar.
[6 marks]
(b)
Explain why xenon has a higher boiling point than fluorine, and why XeF₄ is a solid at room temperature although it is non-polar.
[6 marks]
Total for question 4: 12 marks
5
Lithium hexafluorophosphate, LiPF₆, is the electrolyte in many lithium-ion batteries. It contains the hexafluorophosphate ion, PF₆⁻. If the electrolyte decomposes, the toxic gas phosphorus trifluoride, PF₃, can form. Pauling electronegativity values: P 2.1 and F 4.0.
(a)
What are the shape of the PF₆⁻ ion and the F–P–F bond angle between neighbouring fluorine atoms?
[1 mark]
ATetrahedral, 109.5°
BTrigonal bipyramidal, 90° and 120°
COctahedral, 90°
DSquare planar, 90°
(b)
Which statement about the P–F bonds in PF₆⁻ is correct?
[1 mark]
AEach P–F bond is polar, with the fluorine atom δ−
BEach P–F bond is non-polar because the pair is shared equally
CEach P–F bond is polar, with the phosphorus atom δ−
DThe ion has a permanent dipole because its bonds are polar
(c)
The F–P–F bond angle in PF₃ is about 97°, which is less than 109.5°. Explain why.
[2 marks]
Total for question 5: 4 marks
6
Ethanol, CH₃CH₂OH, and methoxymethane, CH₃OCH₃, are isomers with the same relative molecular mass of 46. Ethanol boils at 78 °C, whereas methoxymethane boils at −24 °C. Propan-1-ol, CH₃CH₂CH₂OH, boils at 97 °C.
(a)
What is the strongest type of intermolecular force between ethanol molecules?
[1 mark]
AInduced dipole–dipole forces
BPermanent dipole–dipole forces
CDative covalent bonds between molecules
DHydrogen bonds
(b)
Which statement best explains why methoxymethane has a much lower boiling point than ethanol?
[1 mark]
AMethoxymethane molecules are non-polar
BMethoxymethane has no hydrogen atom bonded directly to oxygen, so it cannot form hydrogen bonds
CMethoxymethane has weaker covalent bonds
DMethoxymethane has a lower relative molecular mass
(c)
Explain why propan-1-ol has a higher boiling point than ethanol.
[2 marks]
Total for question 6: 4 marks
7
Hydrogen fluoride, HF, and sodium fluoride, NaF, both contain fluorine. Pauling electronegativity values: H 2.1, Na 0.9 and F 4.0. Sodium fluoride melts at 993 °C, whereas hydrogen fluoride boils at 20 °C.
(a)
Explain why the H–F bond is polar and why a molecule of HF has a permanent dipole.
[3 marks]
(b)
Explain why sodium fluoride has a much higher melting point than hydrogen fluoride.
[4 marks]
Total for question 7: 7 marks
8
Boron nitride, BN, exists in a cubic form with a structure like that of diamond, used as a very hard abrasive. Boron atoms have three outer electrons and nitrogen atoms have five. Boron nitride can be made from boron trichloride, BCl₃, and ammonia, NH₃. Pauling electronegativity values: B 2.0, N 3.0 and Cl 3.0.
(a)
Explain why cubic boron nitride is very hard and has a very high melting point, and why each boron atom in it forms four bonds even though boron has only three outer electrons.
[6 marks]
(b)
Explain the shapes and bond angles of BCl₃ and NH₃, and explain why BCl₃ has no permanent dipole.
[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).