Solutions
1) Below are several substances listed in no particular order.
a) NaCl
b) Aluminium metal
c) CO2
d) SiO2
e) Graphite
f) Diamond
g) Nitrogen(N2)
1) Which substance conducts electricity in both the liquid and solid states?
Metals such as aluminium
2) Which substance conducts electricity in only the liquid state?
Ionic compounds such as NaCl.
3) Which substances conduct electricity in only the solid state?
Graphite .
4) Which substance has the lowest melting point?
A molecular substance such as N2
5) Which substance is malleable?
Metals such as aluminium.
6) What substance can be used as a cutting tool for hard rock?
Diamond as it is one of hardest natural substances known.
7) Which two substances are allotropes?
Diamond and graphite.
8) Which two substances contain ions in the solid state?
Metals contain positive ions in a sea of electrons, so aluminium, and ionic substances
such as NaCl.
9) Which two substances contain delocalised electrons in the solid state?
Aluminium and graphite
10) Which substance exists as a gas at room temperature?
Carbon dioxide.
11) Which two substances can be considered as 3D covalent network lattices?
SiO2 and diamond.
12) Dispersion forces play a significant role in which two substances?
In molecular substances such as CO2 and graphite. Dispersion forces act between he
layers of graphite
13) Which three substances have strong covalent intra-molecular bonds but dispersion
forces as the intermolecular bonding force?
CO2 , N2 and graphite. Graphite has strong covalent bonds in 2D layer lattices but
dispersion forces between layers.
14) Which substance has polar covalent intra-molecular bonds and dispersion forces only
as inter-molecular bonds?
CO2 only.
15) Which substance has polar covalent bonding acting in 3D?
SiO2 only.
16) Which substance has pure covalent bonding acting in 3D?
Diamond only.
2)
Draw the molecule in 3D
space, showing all bonding
and non-bonding electrons.
CH4
Inter molecular bonding
Circle the appropriate
response.
Dispersion forces
Intra molecular bonding
NH3
Dispersion forces
Polar covalent
Polar covalent
Dipole-dipole
Hydrogen bonding
H2O
Dispersion forces
Polar covalent
Dipole-dipole
Hydrogen bonding
C2H6
Dispersion forces
Polar covalent
H2
Dispersion forces
Pure covalent
HCl
Dispersion
Dipole-dipole
Polar covalent
3) Dry ice, pictured on the right, is composed of carbon dioxide
molecules.
a) Draw the CO2 molecule indicating all bonding and
Non-bonding electrons.
b) Is the molecule symmetrical ? Yes
c) Is the molecule polar? No
4) Silicon dioxide (SiO2)forms crystals, as pictured on the right.
a) Draw the chemical structure of SiO2 indicating all bonding
and non-bonding electrons where appropriate.
b) Both CO2 and SiO2 sublime at different temperatures. Indicate which has the highest
sublimation temperature and explain why by describing the bonding that exists in the
solid states of both substances. Sio2 has the highest temperature of sublimation as it has
a 3D covalent lattice. This is very strong compared to the dispersion forces that exist
between CO2 molecules.
5) Place the following in order of increasing melting point and explain why.
H2, CH4, C2H6, C3H8.
All the molecules above are symmetrical and therefore non-polar. The inter-molecular bonds
are due to dispersion forces and they differ strength depending on the size of the molecule
(number of electrons present in the molecule).
6) O2 is a bigger molecule than H2O and yet oxygen is a gas at room temperature and water is a
liquid. Explain why?
Water has hydrogen bonding and dispersion forces acting between the molecules, whereas
oxygen only has dispersion forces.
7) Explain why graphite and diamond sublime rather than melt at temperatures around 3825oC
and 4800oC respectively.
Graphite is 2D covalent lattice and diamond is a 3D covalent lattice. When enough heat is
supplied to break the covalent bonds between the carbon atoms it leaves free moving carbon
atoms which form a gas.
8) Two properties of graphite are that it conducts electricity in the solid state and can be used
as a lubricant for heavy machinery. Explain why in terms of its bonding.
Graphite contains delocalised electrons hence it can conduct electricity. The layers are held
together by dispersion forces that can be easily broken and cause the layers to slide over one
another.
9) i)Describe two properties of the precipitate formed when copper sulphate and sodium
carbonate solutions are mixed together.
The precipitate is an ionic substance and therefore has the following properties:
-Conducts electricity in the liquid or aqueous state;
-Brittle;
-Most likely has a high melting temperature;
-insoluble, since it is a precipitate.
ii) Give the formula for the following substances
a) Iron(III) sulphate Fe2(SO4)3
b) Ammonium phosphate (NH4)3PO4
c) Iron(II) phosphate Fe3(PO4)2
10) The valence electrons of four atoms are shown above. Element T, W, Z and Y are found in
period 3 of the periodic table.
a) W and Z react to form a compound.
i)
What is the formula of this compound? WZ2
ii)
Describe the bonding that exists between the particles of this compound.
Ionic bonding
iii)
Draw a simple diagram, in 3d, of the arrangement of particles in the compound.
Label all particles and their charge, if any exist.
b) T and Z react to form a compound
i)
What is the formula of this compound? TZ2
ii)
Describe the bonding that exists between the particles of the compound.
Dipole – dipole and dispersion forces
iii)
Draw a simple diagram, in 3d, of the arrangement of particles in the compound.
Label all particles and their charge, if any exist.
c) Describe the type of bonding found in element W.
Metallic
d) Which elements can conduct electricity in the solid and molten state?
W and Y they are both metals
e) Which group in the periodic table would element W be found?
Group 2
f) Arrange the elements in order of increasing, from lowest to highest, electronegativity
Z, T, W, Y Electronegativity increases across a period.
g) A substance is formed from elements W and Y. Describe the bonding in this substance.
metallic bonding. Positive ions in a sea of delocalised electrons.
h) Which of the following elements can have their physical properties changed by annealing?
W and Y