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Structure
and bonding
Francine
Taylor-Campbell, Contributor
SYLLABUS
REQUIREMENTS
Students
should be able to:
- Define
and give examples of ionic, simple
molecular and giant molecular crystals.
- Explain
the term allotropy.
- Relate
the structure of sodium chloride,
diamond and graphite to their properties.
- Distinguish
between ionic and molecular solids.
2.
Which of the following substances
is an element and forms crystals containing
small molecules?
A.
copper B. graphite C. ice D. iodine
E. sugar
3.
Which statement about graphite is
correct?
A.
It conducts electricity because it
has ions which are free to move.
B.
It has an ionic lattice.
C.
It has the same structure as diamond.
D.
Its structure contains rings of carbon
atoms.
4.
Which substance has the highest melting
point?
A.
diamond B. lead (II) bromide C. methane
D. water
5.
Which statement explains why magnesium
oxide has a very high melting point?
A.
Magnesium atoms and oxygen atoms are
joined by strong double bonds.
B.
The crystal lattice of magnesium oxide
resembles that of diamond.
C.
The magnesium ions are strongly attracted
to the oxide ions.
D.
The reaction between magnesium and
oxygen is strongly exothermic.
ANSWERS
1.
D. Sulphur is a non-metal which
does not conduct electricity. All
other substances can conduct electricity.
The ions in HCl are mobile in solution,
Pb being a metal conducts when solid
and molten, while the ions in NaCl
are able to conduct only when molten
or in solution.
2.
D. Iodine, copper and graphite
(C) are all elements but only iodine
forms small molecules. Sugar and ice
are compounds.
3.
D. The carbon atoms of graphite
are arranged in layers of hexagonal
rings which are able to slide over
each other. Note that graphite conducts
electricity because free electrons,
not ions, are available to carry the
current.
4.
A. Diamond has the highest
melting point because of its macromolecular
structure and the strong covalent
bonds that require a lot of energy
to break. Lead bromide is ionic and
also has high melting points but not
as high as diamond. Methane and water
are simple covalent compounds which
exhibit very low melting points.
5.
C. Magnesium oxide consists of
magnesium and oxide ions which are
strongly attracted to each other.
Breaking this attractive force requires
lots of energy, resulting in a very
high melting point. For this reason
magnesium oxide is used as lining
for furnaces since it can withstand
high temperature without melting or
breaking down.
Francine
Taylor-Campbell is an independent
contributor. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
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