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Index:
Page 3: Covalent Bonding Knowledge Card
Page 4: Separation Techniques Knowledge Card
Page 5: Exam Descriptors/Sample Questions
Page 6: Covalent Bonding & How to draw them
Page 7: Simple & Giant Covalent Compounds
Page 8: Miscible and Immiscible
Page 9: Chromatography
Page 10: Practice exam questions
Page 15: Mark Scheme
Page 18: Sample Question Answers
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Revision Notes
Covalent Compounds and
Separation
Describe what a covalent bond is
Describe the difference between an ionic and covalent
bond, in terms of electrons (3)
Describe what a molecule is
Out of ionic and covalent compounds, which form
lattices and which form molecules? (2)
Draw dot and cross diagrams for
hydrogen, hydrochloric acid, water
and methane
Draw dot and cross diagrams for hydrogen, hydrochloric
acid, water and methane (4)
Draw dot and cross diagrams for
oxygen and carbon dioxide
Draw dot and cross diagrams for oxygen and carbon
dioxide (4)
Explain how to distinguish between
Describe a test to distinguish between an ionic
an ionic and covalent compound
compound and a covalent compound (4)
based on properties
Describe the properties of simple
covalent compounds
Describe the properties of simple covalent compounds
(2)
Explain the properties of simple
covalent compounds
Explain why simple covalent compounds have low
melting points and don't conduct (4)
Describe the properties of giant
covalent compounds
Describe the properties of giant covalent compounds
(2)
Explain the properties of giant
covalent compounds
Explain why giant covalent compounds don't conduct
electricity and have a high melting point (4)
Explain, in terms of structure, the
difference in uses between
graphite and diamond
Explain why diamond is used in tool cutters, whilst
graphite is used in pencils and as electrodes (6)
Explain the difference in properties
of ionic and covalent compounds
Explain why ionic compounds can conduct only when
molten, but covalent compounds cannot conduct at all
(4)
Describe how to separate two
immiscible liquids
How can you separate the immiscible oil and water? (2)
Explain how to separate two
miscible liquids, such as the gases
in air
Describe, step by step, how you would separate a
miscible mixture of air (nitrogen, oxygen and carbon
dioxide) (4)
Describe how to carry out paper
chromatography to separate inks
Describe how to prepare a chromatogram for an
unknown ink (3)
Explain the results of
In a sample chromatogram, blue ink travels 2.4cm, red
chromatograms by determining the ink travels 4.5cm and the water travelled 10cm.
Rf
Calculate the Rf values for both inks. (3)
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Section 1: Covalent Compounds
Covalent bonding is the sharing of pairs of electrons between
two non-metals
Non-metals need extra electrons to get a full outer shell. Neither can give their electrons up, so
they share.
For example, both hydrogen and chlorine need one electron to get a full outer shell. So one
electron from each element overlaps to ensure that hydrogen has 2 electrons in its shell, and
chlorine has 8 electrons in its shell.
How to draw covalent bonds:
Example: Methane, CH4.
Step 1: Look at which group they are in to find out how many electrons they need to fill their
outer energy shell. Carbon needs 4 and hydrogen needs 1.
Step 2: The number of electrons needed is the number of
each element can have. Hydrogen can only bond once, and
bond four times. Think of it like this:
bonds that
carbon can
Step 3: Draw the central atom – in this case
Spread the electrons evenly.
carbon.
Step 4: For each bond needed, add one of
hydrogen’s, overlapping to ensure that every
paired up.
your
electron is
Step 5: Check! Make sure each atom has a full outer shell! If not, go back and try again!
Section 2: Alkali Metals
All of the alkali metals, in group 1, are soft and highly reactive – which is unusual because
most metals are strong and quite unreactive.
Their reactivity increases as you go down the group.
They react with water to make hydroxides, and oxygen to make oxides – these are alkaline
substances with a pH of 8 and above. They usually turn universal indicator purple.
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Section 2: Types of Covalent Compounds
Simple Covalent Structures:
Simple covalent molecules have strong covalent bonds, but only have low boiling points
because there are weak intermolecular forces, which don’t require much energy to break:
Giant Covalent structures:
Giant covalent structures also have covalent bonds, which are strong. They do not have
intermolecular forces here, and therefore a lot of energy is needed to break the bonds.
Therefore they have high melting points.
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Section 3: Separation Techniques
If you wanted to separate air – which is miscible – you would cool it down to -200oC and carry
out distillation like above.
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Section 4: Chromatography
Chromatography can be used to separate mixtures of coloured compounds. Mixtures that
are suitable for separation by chromatography include inks, dyes and colouring agents in food.
Setting up a chromatogram:
Simple chromatography is carried out on paper. A spot of the mixture is placed near the
bottom of a piece of chromatography paper and the paper is then placed upright in a suitable
solvent, eg water.
The solvent is the liquid that will dissolve the dye/ink.
As the solvent soaks up the paper, it carries the mixtures with it. Different components of the
mixture will move at different rates. This separates the mixture out.
Retention Factor, Rf:
Different chromatograms and the separated components of the mixtures can be identified by
calculating the Rf value using the equation:
Rf = distance moved by the compound ÷ distance moved by the solvent
The Rf value of a particular compound is always the same - if the chromatography has been
carried out in the same way. This allows industry to use chromatography to identify
compounds in mixtures.
In this example, the unknown sample is an impure mixture of two inks – blue and yellow.
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Q1. Covalent Compounds
diagram shows part of the structure of diamond.
Complete the sentences by putting a cross (
next to your answer.
The
) in the box
(i) The bonds between carbon atoms in diamond contain
(1)
A
B
C
D
protons
neutrons
electrons
ions
(ii) The structure of diamond is
(1)
A
B
C
D
simple molecular, covalent
giant molecular, covalent
ionic
metallic
(iii) Describe what is meant by a covalent bond.
(2)
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Q2. The drink contained water.
Complete the dot and cross diagram for water by adding the electrons of the hydrogen atoms.
(1)
Q3.
The atomic number of carbon is 6 and of fluorine is 9.
Carbon and fluorine atoms are combined in a tetrafluoromethane molecule, CF 4.
Draw a dot and cross diagram of a tetrafluoromethane molecule.
Show outer electrons only.
(2)
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Q4. Draw a dot and cross diagram of a molecule of hydrogen chloride. Show outer electrons
only.
(2)
Q5. Oxygen is a simple molecular, covalent substance.
(i) The electronic configuration of oxygen is 2.6.
Draw a dot and cross diagram for a molecule of oxygen, O2.
Show the outer electrons only.
(3)
Q6. Properties of Covalent Compounds
(a) Complete the sentence by putting a cross (
A property of hydrogen chloride is that it
) in the box next to your answer.
(1)
A
B
C
D
conducts electricity
has a high melting point
has a low boiling point
exists as a giant structure
(b) The diagram shows part of the structure of diamond.
How many bonds does a typical carbon atom in diamond form?
(1)
........................................................................................................
(c) Nitrogen and oxygen are present in the air.
Oxygen has a low boiling point because there are
(1)
A
B
C
D
weak covalent bonds between the oxygen atoms
weak covalent bonds between the oxygen molecules
weak forces of attraction between the oxygen atoms
weak forces of attraction between the oxygen molecules
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(d) Carbon dioxide is a gas at room temperature.
A carbon dioxide molecule is a
(1)
A
B
C
D
giant molecule that has covalent bonds
giant molecule that has ionic bonds
simple molecule that has covalent bonds
simple molecule that has ionic bonds
Q7. Structures
The table shows some properties of diamond and
graphite.
(i) Suggest why diamond and graphite might be
expected to have similar properties.
(1)
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(ii) By referring to its structure, explain why diamond is very hard.
(3)
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(iii) By referring to its structure, explain why graphite flakes easily.
(2)
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Q8. (a) The apparatus shown can be used to test
the electrical conductivity of liquids.
Describe how you would use this apparatus to
show that the electrical conductivity of hexane is
that of a typical simple molecular, covalent
compound.
(2)
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(b) Methane is a gas at room temperature. It exists as molecules, CH4.
Methane has a low boiling point. It does not conduct electricity.
Explain, in terms of the nature of its molecules and the forces between its molecules, why
methane has a low boiling point and does not conduct electricity.
(6)
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Q9. Separating Techniques
(a) Complete the sentence by putting a cross (
) in the box next to your answer.
A mixture of two immiscible liquids can be separated by using
(1)
A
B
C
D
fractional distillation
a separating funnel
evaporation
filtration
(b) Describe how you can use the apparatus named in part (a) to separate an immiscible mixture of
oil and water.
(1)
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(c) Describe how oxygen and nitrogen are obtained from liquid air by fractional distillation.
(3)
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Q10. Chromatography
(a) Some food colourings are a mixture of
coloured substances.
Charles carried out a chromatography
experiment to test which food colouring was
present in a coloured drink.
He used samples of three food colourings, X,
and Z.
Y
He also tested a sample of the colouring in
drink.
the
(i) Charles looked at the chromatogram above to find out which food colourings contained more
than one coloured substance.
State all the food colourings that contain more than one coloured substance.
(1)
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(ii) Food colouring Y is banned.
Explain how Charles can tell that the drink that he tested did not contain the banned food
colouring.
(2)
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(iii) Calculate the Rf value for the coloured substance in food colouring X.
(2)
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Rf = . . . . . . . . . . . . . . . . . . . . .
(b) Describe in detail how the experiment should be carried out to produce the chromatogram
shown in (a).
(6)
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Q1.
(i)
(ii)
(iii)
Q2.
Answer
C
B
An description including
 shared (electrons) (1)
pair(s) of electrons (between
atoms) (1)
Acceptable answers
Mark
(1)
(1)
Ignore reference to complete/full shells
Ignore reference to between two
metals
Ignore reference to between metal and
non-metal
Ignore reference to between molecules
Any reference to between ions scores 0 (2)
Answer
Acceptable answers
2 electrons to be drawn in, one
between each hydrogen and
oxygen atom in the overlap region
or on the overlapping circles
Ignore an inner shell on the oxygen
if it has 2 electrons Do not award
the mark if additional atoms or
electrons added to the diagram
dots/crosses/circles/ e/e- for
electrons
Q3. Answer
Acceptable answers
• four bonding pairs shown (1)
• six non bonded electrons on
each fluorine atom (1)
Answer
Acceptable answers
Mark
(1)
Mark
(2)
Mark
Q4.
(2)
Allow a diagram without labels for
2 marks
any symbols shown
must be correct for the 2nd mark
shared pair in allow any combination of dots
molecule (1)
and crosses for electrons wrong
rest of molecule consequent on
compound = zero marks
first mark (1)
Answer
Acceptable answers
Mark
Q5.
(i)
(3)
 electrons shared / between
atoms (1)
 2 pairs of/four electrons
shared / between two atoms (1)
 4 additional electrons on both
oxygen atoms (1)
ignore any inner electrons
shown
3rd Mark is dependent on 2nd
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Q6.
Answer
Acceptable answers
(a)
(b)
(c)
Mark
C has a low boiling point
(1)
four/4
(1)
D weak forces of attraction between the
(1)
oxygen molecules
(d)
C
(1)
Q7.
Answer
Acceptable Mark
(i)
both (pure forms of) carbon / both giant molecular
(1)
(ii)
An explanation linking three of the following points
• (every) carbon atom forms four bonds (1) • strong
bonds / hard to separate atoms from lattice (1)
• covalent bonds (1) • no weaknesses in molecule (1)
(3)
(iii)
An explanation linking the following • (in) layers (1)
• weak forces between layers (1)
(2)
Q8.
Answer
Acceptable Mark
(a)
A description including two of the following points • test
circuit first to ensure bulb lights • pour hexane / liquid
into beaker(1) • bulb does not light(1) • (liquid)does
not conduct (electricity)(1)
(2)
(b) A description including some of the following points
Molecules: simple / small molecule
separate / discrete molecules
covalent bonds (between atoms in molecule)
displayed structure for CH4
weak forces between molecules
Properties: to boil need to separate molecules
little energy needed (as weak forces between molecules)
therefore low boiling point
to be able to conduct must have charged particles
which must be free to move
no charged particles present
no delocalised /free electrons / no ions present
all electrons are in covalent bonds
therefore does not conduct electricity / cannot carry current
(6)
Level
No rewardable content
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1 - 2  a limited description
e.g. methane is a simple / small molecule
e.g. weak forces between molecules
2
3 - 4  a simple description
e.g. methane is a simple / small molecule with weak forces between
molecules (so low boiling point)
e.g. it is covalent / there are no charged particles (ions or free
electrons) to move and carry the current
3
5 - 6  a detailed description
e.g. methane is a simple / small molecule with weak forces between
molecules (so low boiling point) AND any mention of lack of charged
particles
e.g. does not conduct electricity because it is covalent /there are no
charged particles (ions or free electrons) to move and carry the current
AND any mention of separate molecules or weak forces between them
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Q9
(a)
(b)
Q10
(a)
(i)
(a)
(ii)
(a)
(iii)
Answer
Acceptable answers
B
A description linking use
separating funnel (1)
run off
lower layer / liquid / OWTTE (1)
alternative description of
separating funnel eg funnel with a
tap at the bottom suitable labelled
diagram burette allow layers /
liquids to separate ignore
fractional distillation
A description including three from
 (liquid air enters) (fractionating)
column (1)
 (liquid air) warms/heats/boils (1)
 (gaseous) nitrogen/lower boiling
point from top of column (1)
 (liquid) oxygen/higher boiling
point from bottom of column (1)
Answer
Y and Z
both must be given with no
additional substances
An explanation linking two of
only one coloured substance in
drink/ only one spot (at 4) in drink (1)
this is not present in Y/ no spot at
4 in Y/ no corresponding spot in Y
(1)
the spots would rise to the same
point if they were the same
substance / the drink is X (1)
two coloured substances in Y/ Y
has 2 spots (at 2.5 and 7) (1)
drink does not have spot(s)
corresponding to spot(s) in Y (1)
(spot moved) 4 ± 0.5 / solvent
(moved) 8 (1) Rf = 4/8 (2) (=0.5)
consequential on their value for spot
moved
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Mark
(1)
(2)
(3)
ignore references to cooling air
etc.
can be separated because they
have different boiling points (1)
alternative to last two marking
points
Acceptable answers
Mark
(1)
(2)
allow values ± 0.5 of those given
here
Y has more than 1
coloured substance/spot do not
allow a specified number greater
than 2
(2)
4/8 OR 0.5 on its own (2)
8/4 (1)
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Question:
Describe the difference between an ionic and
covalent bond, in terms of electrons (3)
Out of ionic and covalent compounds, which form
lattices and which form molecules? (2)
Draw dot and cross diagrams for hydrogen,
hydrochloric acid, water and methane (4)
Draw dot and cross diagrams for oxygen and carbon
dioxide (4)
Describe a test to distinguish between an ionic
compound and a covalent compound (4)
Describe the properties of simple covalent
compounds (2)
Explain why simple covalent compounds have low
melting points and don't conduct (4)
Describe the properties of giant covalent compounds
(2)
Explain why giant covalent compounds don't conduct
electricity and have a high melting point (4)
Explain why diamond is used in tool cutters, whilst
graphite is used in pencils and as electrodes (6)
Explain why ionic compounds can conduct only when
molten, but covalent compounds cannot conduct at
all (4)
How can you separate the immiscible oil and water?
(2)
Describe, step by step, how you would separate a
miscible mixture of air (nitrogen, oxygen and carbon
dioxide) (4)
Describe how to prepare a chromatogram for an
unknown ink (3)
In a sample chromatogram, blue ink travels 2.4cm,
red ink travels 4.5cm and the water travelled 10cm.
Calculate the Rf values for both inks. (3)
Model Answer:
Ionic bonding is where metals donate/give electrons
(1) to non metals, which receive/accept them (1).
Covalent bonding is a shared pair of electrons (1)
Ionic = lattice (1). Covalent = molecules (1)
Check the revision guide for each, or the covalent
bonding board
Check the revision guide for each, or the covalent
bonding board
Dissolve them in water (1). Add electrodes connected
to a circuit (1). It if lights up, it is ionic (1), if not it is
covalent (1)
Low melting points (1) and don't conduct (1)
Low melting points: Weak intermolecular forces /
weak forces between the molecules (1) which don't
need much energy to break (1)
Don’t conduct: No spare electrons (1) to carry on a
charge (1)
High melting points (1) and don't conduct (1)
High melting points: lots of strong covalent bonds (1)
which need a lot of energy to break (1)
Don’t conduct: No spare electrons (1) to carry on a
charge (1)
Diamond: Forms four (1) strong (1) covalent bonds (1),
making it hard (1)
Graphite: Forms three strong covalent bonds (1). One
spare electron (1) which can move (1) and carry a
charge ← electrode. Has layers (1) which can slide (1)
← lubricant
Ionic: When molten, the ions (1) are free to move (1).
Covalent: No spare electrons (1) that are free to move
(1)
Separating funnel (1) turn the tap (1)
Cool down to -200 degrees (1). Remove carbon dioxide
and water (1). Start to warm back up. Nitrogen will
become a gas first and can be collected at the top (1).
Oxygen stays a liquid (1)
Draw a line and add a cross in pencil at the bottom of
the chromatography paper (1). Add a dot of the ink
and add to water (1). The water will move up the
paper, moving the ink up the paper (1)
Blue Rf = 2.4 / 10 = 0.24 (1). Red Rf = 4.5/10 = 0.45 (1)
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