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.
2. The first twenty elements can be arranged according to bonding and
structure.
aluminium
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.
3. Compounds can have different structures and properties.
(they have the same
electronegativity)
3. SiO2
NH4NO3
SiO2
BaSO4
K2O
Na2CO3
P2O5
Identify the compound with a covalent network structure.
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
4. (a) FeS + 2HCl  FeCl2 + H2S
(b) Hydrogen.
5. (a) Hydrogen fluoride.
(b) Hydrogen and phosphorus.
lithium hydride
phosphorus
hydrogen fluoride
sodium
hydrogen iodide
(a) Identify the substance with hydrogen bonding between the
molecules.
(b) Identify the two substances with pure covalent bonding in the
molecules.
6.
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. (a)
(b)
Van der Waals forces.
Hydrogen fluoride is a highly polar molecule. Fluorine
atoms have a higher electronegativity (attraction for
shared electrons) than hydrogen atoms. In the H-F bond
the fluorine atoms have slight negative charge and the
hydrogen atoms a slight positive charge. These charges
result in neighbouring molecules be attracted to each
other by hydrogen bonds to form double and triple
molecules.
In F2 and H2 molecules the molecules a non-polar and so
there is only the weak van der Waals attraction which is
not strong enough to form double and triple molecules.
7. Name the structure and type of bonding in silicon dioxide.
Covalent network.
8.
Type B
Type E
Type C
Type D
Type A
Which type of element A to E shown above is
(a)
Monatomic gases?
(a)
Type E
(b)
Covalent network solids?
(b)
Type B
(c)
Diatomic covalent gases?
(c)
Type D
(d)
Discrete covalent molecular solids?
(d)
Type C
(e)
Metallic lattice solids?
(e)
Type A