Edexcel Chemistry Topic 3
Edexcel Chemistry Topic 3
Edexcel Chemistry Topic 3
ASSESSED HOMEWORK
Answer all questions
Max 80 marks
Name
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1. The table below shows the boiling points of some hydrogen compounds formed
by Group 6 elements.
HO 2 HS 2 H Se
2 H Te
2
(a) State the strongest type of intermolecular force in water and in hydrogen
sulfide (H S). 2
Water ...........................................................................................................
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(2)
(b) Draw a diagram to show how two molecules of water are attracted to each
other by the type of intermolecular force you stated in part (a). Include partial
charges and all lone pairs of electrons in your diagram.
(3)
(c) Explain why the boiling point of water is much higher than the boiling point of
hydrogen sulfide.
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(1)
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(2)
Name the type of bond formed when H ions react with H O molecules.
+
2
Explanation ..................................................................................................
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(2)
Predict the type of bonding in sodium sulfide and explain why its melting point
is high.
Explanation ..................................................................................................
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(3)
(Total 13 marks)
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(ii) Explain why magnesium has a higher melting point than sodium.
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(4)
(b) Why do diamond and graphite both have high melting points?
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(3)
(c) Why is graphite a good conductor of electricity?
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(1)
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(2)
(Total 10 marks)
3. (a) The shape of the molecule BCl and that of the unstable molecule CCl are
3 2
shown below.
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(ii) Predict the bond angle in CCl and explain why this angle is different
2
Explanation .........................................................................................
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(5)
(b) Give the name which describes the shape of molecules having bond angles of
109° 28'.
Give an example of one such molecule.
Example .......................................................................................................
(2)
(c) The shape of the XeF molecule is shown below.
4
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(ii) Suggest why the lone pairs of electrons are opposite each other in this
molecule.
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(iii) Name the shape of this molecule, given that the shape describes the
positions of the Xe and F atoms only.
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(4)
(d) Draw a sketch of the NF molecule. Indicate in your sketch any lone pairs of
3
electrons on nitrogen.
(2)
(Total 13 marks)
4. The table below shows some values of melting points and some heat energies
needed for melting.
Substance I 2 NaCl HF HCl HI
Force 1 ........................................................................................................
Force 2 ….....................................................................................................
Force 3 ….....................................................................................................
(3)
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(4)
(c) In terms of the intermolecular forces involved, suggest why
(i) hydrogen fluoride requires more heat energy for melting than does
hydrogen chloride,
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(ii) hydrogen iodide requires more heat energy for melting than does
hydrogen chloride.
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(5)
(d) (i) Explain why the heat energy required to melt sodium chloride is large.
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(ii) The heat energy needed to vaporise one mole of sodium chloride (171
kJ mol ) is much greater than the heat energy required to melt one mole
–1
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(3)
(e) In terms of its structure and bonding, suggest why graphite has a very high
melting point.
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(2)
(Total 17 marks)
5. Sodium sulphide, Na S, is a high melting point solid which conducts electricity
2
electricity.
Bonding in Na S ..................................................................................
2
Bonding in CS .....................................................................................
2
(ii) By reference to all the atoms involved explain, in terms of electrons, how
Na S is formed from its atoms.
2
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(iii) Draw a diagram, including all the outer electrons, to represent the
bonding present in CS 2
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(7)
(Total 7 narks)
6. (a) Both HF and HCl are molecules having a polar covalent bond. Their boiling
points are 293 K and 188 K respectively.
(i) State which property of the atoms involved causes a bond to be polar.
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(4)
(b) When aluminium chloride reacts with chloride ions, as shown by the equation
below, a co-ordinate bond is formed.
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(2)
(c) Draw the shape of the PCl molecule and of the PCl ion. State the value(s) of
5 4
+
(a) Give the name of the type of bond formed when phosphine reacts with an H +
Explanation ..................................................................................................
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(3)
(b) Draw the shapes, including any lone pairs of electrons, of a phosphine
molecule and of a phosphonium ion.
Give the name of the shape of the phosphine molecule and state the bond
angle found in the phosphonium ion.
PH
3
SECTION B
8. Which one of the following ions has three lone pairs of electrons around the central
atom?
A BF
B NH
C ClF
D PF
(Total 1 mark)
10. Which one of the following has the most covalent character?
A MgF2
B MgBr2
C AlF3
D AlBr3
(Total 1 mark)