Answers:
LEVEL: AS
CHEMISTRY – Atoms, ions and molecules
3. Electronic configurations, bonding and properties of ionic and covalent
structures (15 minutes)
(a) Write the ground state electronic configurations, in terms of s, p and d electrons, for each of
the following isolated species:
(i) A chlorine atom.
(1 mark)
Cl 1s22s22p63s23p5
(ii) A calcium ion.
(1 mark)
Ca 1s22s22p63s23p64s2
(b) State two general characteristics of ionic compounds.
(2 marks)
They are brittle crystalline solids that can be cleaved and have high melting points.
(c) Describe the difference between the structures of sodium chloride and caesium chloride.
Your answer may be either a written description or clearly labelled diagrams.
(i) Sodium chloride:
(2 marks)
In sodium chloride, each ion is surrounded by six of the oppositely charged ions. Sodium chloride has a
double interlocking face-centred cubic structure.
Copyright © Pearson Education Limited 2001
1
Answers:
LEVEL: AS
CHEMISTRY – Atoms, ions and molecules
(ii) Caesium chloride:
(2 marks)
In caesium chloride, each ion is surrounded by eight of the oppositely charged ions. Caesium chloride
has a double interlocking simple cubic structure.
TIP: Avoid taking up time drawing complicated diagrams when a simple one will do!
(d) (i) Draw a dot and cross diagram to represent each of the following covalent molecules:
ammonia, NH3, carbon dioxide, CO2.
(4 marks)
ammonia, NH3
carbon dioxide, CO2
(ii) Use the electron pair repulsion theory to deduce and draw the shape of each molecule.
(4 marks)
ammonia, NH3
3 shared and 1 unshared pair
of electrons mutually repel to
give pyramidal shape
carbon dioxide, CO2
2 double bonds mutually repel
to give linear shape
(e) Explain, in terms of the forces between atoms and molecules, why a diamond crystal is hard
and an iodine crystal is soft.
(3 marks)
In a diamond crystal, all the carbon atoms are strongly held together by four covalent bonds per atom
into one giant three-dimensional structure. In an iodine crystal, pairs of atoms are strongly held
together by single covalent bonds into diatomic molecules but these small molecules are attracted to
each other only by weak van der Waals' forces.
(Total marks 19)
Copyright © Pearson Education Limited 2001
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