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Structure
and bonding
Francine
Taylor-Campbell, Contributor
In
this lesson, we will attempt a few
questions on the topic.
QUESTION
1
(a)
Answer the questions concerning the
solid substances A to D, the identities
of which are given below:
A
– graphite,
B
– diamond,
C – carbon dioxide,
D
– sodium chloride
(b)
Name the type(s) of bonding to be
found in A. (1 mark)
(c)
Explain why A conducts electricity
but B and D do not. (3 marks)
(d)
Why does B have a higher melting point
than C? (2 marks)
(e)
Compare the hardness of A and B.
(2 marks)
ANSWERS
(a)
Graphite is made up of carbon atoms
bonded together by strong covalent
bonds. These bonds extend throughout
the whole structure.
(b)
Graphite conducts electricity because
electrons can move about in each layer.
These electrons are said to be delocalised.
Diamond, on the other hand, has no
‘free’ electrons while sodium
chloride has no ‘free’ or
mobile ions.
Comment:
For substances to conduct electricity,
ions or electrons must be able to
move so that the charge can be carried
throughout the entire substance. All
the valence electrons on carbon are
involved in bonding. In sodium chloride,
the ions are held in position and
are free to move only if molten or
in solution.
(c)
The carbon atoms in B are held by
strong covalent bonds which are hard
to break and require vast amounts
of energy. In C, solid carbon dioxide
molecules of CO2 are joined together
by weak forces of attraction between
the molecules. B, therefore, has a
higher melting point than C.
(d)
A (graphite) consists of carbon atoms
arranged hexagonally in layers, with
weak forces of attraction between
layers. This makes it soft, as the
layers can slide over each other.
The carbon atoms in B are arranged
tetrahedrally and are held by very
strong covalent bonds throughout.
QUESTION
2
2.
Compare calcium and carbon (include
allotropes) by referring to:
(a)
their physical properties
(b)
their electrical properties
(c)
the chemical properties of their oxides
(d)
the types of bonds present in their
chlorides
(5
marks)
ANSWERS
(a)
Calcium has high melting and boiling
points due to the strong bonds formed
between cations and the ‘sea’
of mobile electrons. Carbon, in the
form of graphite and diamond, has
strong bonds which also result in
high melting and boiling points. These
substances are also solids at room
temperature, owing to these strong
bonds.
(b)
The mobile or delocalised electrons
in calcium and graphite make them
good conductors of heat and electricity.
Diamond will not conduct heat or electricity
since it has no free electrons.
(c)
Calcium oxide (CaO) is a basic oxide
and will dissolve in water to form
an alkaline solution (calcium hydroxide).
It also reacts with acids to form
salt and water.
CaO(s)
+ H2O(l) = Ca(OH)2
(aq) (Alkaline solution).
CaO
(s) + H2SO4(aq)
= CaSO4(aq) + H2O
(l)
Carbon
dioxide is an acidic oxide and reacts
with water to form acids.
CO2(g)
+ H2O(l) = H2CO3
(aq) Carbonic acid carbon monoxide
is a neutral oxide and is a good reducing
agent, reducing zinc and metals below
it in the reactivity series.
CuO
(s) + CO (g) = Cu (s) + CO2 (Reducing
agent).
(d)
Calcium chloride (CaCl2)
has ionic bonds present in its structure,
while covalent bonds are present in
carbon tetrachloride (CCl4).
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This
is the final stage in the creation
of something beautiful during
art class.
- contributed
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Francine
Taylor-Campbell is an independent
contributor.
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