HIGHER CHEMISTRY REVISION.

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HIGHER CHEMISTRY REVISION.
Unit 1- Bonding, Structure and Properties
1. Although propane and ethanol have similar
molecular masses, the alkane is a gas at
room temperature while the ethanol is a liquid.
This difference in boiling point is due to
the different strengths of the
intermolecular forces in the two compounds.
Explain why propane is a gas at room temperature
while ethanol is a liquid. In your
answer you should name the intermolecular forces
involved in each compound and explain how
they arise.
1. In propane there are only weak van der Waals
attractions between the non-polar propane
molecules. It takes very little energy to
break these van der Waals attractions and so
propane has a low boiling point. In
ethanol there is a polar O-H group. The oxygen
atom has a higher electronegativity
(attraction for electrons) than the hydrogen
. This results in the shared electrons in the O
to H bond being attracted towards the oxygen
giving it a slight negative charge. The
hydrogen has a slight positive charge. There is
an attraction between the opposite charges
in neighbouring molecules which means more
energy this is known as hydrogen bonding.
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2. The first twenty elements can be arranged
according to bonding and structure. alumin
ium boron chlorine hydrogen
phosphorus silicon (a) Identify the element
which is a discrete molecular solid at room
temperature and pressure. (b) Identify the two
elements which combine to form the compound with
the most covalent character. (You
may wish to use page 10 of the data booklet.)
2. (a) Phosphorus. (b) Phosphorus and
hydrogen. (they have the same
electronegativity) 3. SiO2
3. Compounds can have different structures and
properties. NH4NO3 BaSO4
Na2CO3 SiO2 K2O P2O5
Identify the compound with a covalent network
structure.
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4. Hydrogen sulphide, H2S, is an unpleasant gas
produced when eggs rot. (a) The gas can be
prepared by the reaction of iron(II) sulphide
with dilute hydrochloric acid.
Iron(II) chloride is the other product of the
reaction. Write a balanced chemical
equation for this reaction. (b) Iron metal is
often an impurity in iron(II) sulphide.
Name the other product which would be formed in
the reaction with dilute hydrochloric
acid if iron metal is present as an impurity.
5. The properties of substances depends on their
structures and bonding. hydrogen phosphorus
sodium lithium hydride
hydrogen fluoride hydrogen iodide
(a) Identify the substance with hydrogen
bonding between the molecules.
(b) Identify the two substances with pure
covalent bonding in the molecules.
4. (a) FeS 2HCl ? FeCl2 H2S (b)
Hydrogen. 5. (a) Hydrogen fluoride. (b)
Hydrogen and phosphorus.
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A mass spectrometer is an instrument that can be
used to gain information about the masses of
molecules. When hydrogen fluoride is analysed in
a mass spectrometer as well as molecules with a
relative molecular mass of 20, some double
molecules (relative molecular mass 40) and
triple molecules (relative molecular mass 60)
are found to exist. No such molecules are found
when the elements hydrogen and fluorine, are
separately analysed. (a) Name the weak force of
attraction between molecules that is found in
both liquid hydrogen and liquid fluorine. (b)
Why are double and triple molecules found in
hydrogen fluoride but not in hydrogen and
fluorine?
6.
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7. Name the structure and type of bonding in
silicon dioxide.
Covalent network.
8.

• Which type of element A to E shown above is
• Monatomic gases?
• Covalent network solids?
• Diatomic covalent gases?
• Discrete covalent molecular solids?
• Metallic lattice solids?

• Type E
• Type B
• Type D
• Type C
• (e) Type A