Bonding and StructureEdexcel International A Level Chemistry: Topic test

20 questions, 54 marks

Edexcel International A Level Chemistry

Bonding and Structure topic test

Total 54 marks

Name

Class

Date

1
The ions O²⁻, F⁻, Na⁺ and Mg²⁺ each have the electronic configuration 1s²2s²2p⁶. Their ionic radii are: O²⁻ 0.140 nm, F⁻ 0.133 nm, Na⁺ 0.102 nm and Mg²⁺ 0.072 nm. Magnesium oxide melts at 2852 °C and sodium fluoride melts at 993 °C.
(a)
Which statement explains why the ionic radius decreases from O²⁻ to Mg²⁺?
[1 mark]
AThe ions have the same number of electrons but an increasing number of protons, so the electrons are attracted more strongly
BThe ions have an increasing number of electron shells
CThe ions have a decreasing number of electrons
DRepulsion between the electrons increases from O²⁻ to Mg²⁺
(b)
What is the main reason that magnesium oxide melts at a much higher temperature than sodium fluoride?
[1 mark]
AMagnesium oxide contains covalent bonds between its molecules
BMg²⁺ is larger than Na⁺, so the ions pack more tightly
CThe ions in magnesium oxide have higher charges, so the electrostatic attraction between ions is stronger
DMagnesium oxide ions have different electronic configurations from sodium fluoride ions
(c)
Predict whether the ionic radius of S²⁻ is larger or smaller than that of O²⁻, and explain your answer.
[2 marks]
Total for question 1: 4 marks
2
Ionic radii: Be²⁺ 0.031 nm, Mg²⁺ 0.072 nm, Ca²⁺ 0.100 nm, Na⁺ 0.102 nm, F⁻ 0.133 nm, Cl⁻ 0.181 nm, Br⁻ 0.196 nm and I⁻ 0.220 nm. Beryllium chloride has some covalent character, but calcium chloride is almost completely ionic.
(a)
Which cation has the greatest polarising power?
[1 mark]
ANa⁺
BMg²⁺
CCa²⁺
DBe²⁺
(b)
Which anion is the most polarisable?
[1 mark]
AF⁻
BI⁻
CCl⁻
DBr⁻
(c)
Explain why beryllium chloride has more covalent character than calcium chloride.
[2 marks]
Total for question 2: 4 marks
3
Boron trifluoride, BF₃, reacts with ammonia, NH₃, to form a single compound, F₃B–NH₃, in which the boron atom has four bonds.
(a)
Explain how a dative covalent bond forms between the boron and nitrogen atoms.
[3 marks]
(b)
Predict the shape of the BF₃ molecule and the bond angle in it, and explain why the shape around the boron atom changes when F₃B–NH₃ forms.
[4 marks]
Total for question 3: 7 marks
4
In the electrolysis of molten sodium chloride, current is carried through the electrolyte by ions and the electrodes are made of graphite. Sodium chloride melts at 801 °C, sodium metal melts at 98 °C, and graphite sublimes at about 3600 °C. Diamond does not conduct electricity.
(a)
Explain, in terms of structure and bonding, why solid sodium chloride does not conduct electricity but molten sodium chloride does, and why graphite conducts electricity but diamond does not.
[6 marks]
(b)
Explain why sodium metal melts at a much lower temperature than sodium chloride, and why sodium chloride melts at a lower temperature than the temperature at which graphite sublimes.
[6 marks]
Total for question 4: 12 marks
5
Pauling electronegativity values: C 2.55, S 2.58, Si 1.90, Cl 3.16 and Mg 1.31. Silicon tetrachloride, SiCl₄, is a tetrahedral molecule, and carbon disulfide, CS₂, is a linear molecule, S=C=S. Magnesium chloride is an ionic compound.
(a)
Which bond is the most polar?
[1 mark]
AC–S
BSi–Cl
CC–Cl
DS–Cl
(b)
Why is the SiCl₄ molecule non-polar although each Si–Cl bond is polar?
[1 mark]
AThe Si–Cl bonds are not polar because silicon and chlorine are both non-metals
BThe chlorine atoms are all the same, so the molecule has no dipoles
CThe lone pairs on silicon cancel the dipoles
DThe four bond dipoles are arranged symmetrically in a tetrahedron and cancel
(c)
Define electronegativity, and explain why the bonding in magnesium chloride is ionic.
[2 marks]
Total for question 5: 4 marks
6
Phosphorus, in Group 15 directly below nitrogen, forms phosphine, PH₃. Phosphine reacts with strong acids to form the phosphonium ion, PH₄⁺. Silicon forms SiH₄ and sulfur forms H₂S. Assume that these species have shapes analogous to those of similar species of the elements above them.
(a)
What is the shape of a phosphine molecule, PH₃, and its approximate H–P–H bond angle?
[1 mark]
ATrigonal planar, with an angle of 120°
BTetrahedral, with an angle of 109.5°
CTrigonal pyramidal, with an angle less than 109.5°
DBent, with an angle of about 104.5°
(b)
Which of these species has a tetrahedral shape with bond angles of 109.5°?
[1 mark]
APH₄⁺
BPH₃
CH₂S
DPCl₅
(c)
Explain why the H–P–H bond angle in PH₃ is smaller than the bond angle in PH₄⁺.
[2 marks]
Total for question 6: 4 marks
7
Tungsten is used as the filament in some lamps and has a melting temperature of 3422 °C. Caesium, in the same part of the Periodic Table as sodium, melts at 28.5 °C. Both are metals with a high electrical conductivity.
(a)
Describe the bonding in a metal such as tungsten and use it to explain why metals conduct electricity.
[3 marks]
(b)
Explain why tungsten melts at a much higher temperature than caesium, and why this makes tungsten suitable for a lamp filament.
[4 marks]
Total for question 7: 7 marks
8
Hydrogen chloride gas dissolves in water to form hydrochloric acid, in which the hydronium ion, H₃O⁺, is present. Pauling electronegativity values: H 2.20, Cl 3.16 and K 0.82.
(a)
Explain how a hydronium ion, H₃O⁺, forms from a water molecule and a hydrogen ion, H⁺. Predict the shape of H₃O⁺ and its bond angle, and explain why the angle is not 109.5°.
[6 marks]
(b)
Define electronegativity. Then use the electronegativity values to explain why the bond in hydrogen chloride is polar covalent, why the bond in a chlorine molecule is non-polar, and why potassium chloride is ionic. Describe how these examples show that ionic and covalent bonding are the extremes of a continuum.
[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).