IGCSEScienceEdexcelScience (Double Award) (Modular)Chemistry Unit 2Exam Questions5. Principles of Chemistry: Part 2Covalent bonding

Covalent bonding (Edexcel IGCSE Science (Double Award) (Modular): Chemistry Unit 2): Exam Questions

Exam code: 4XSD1

2 hours18 questions
Easy
Medium
Hard
1
1 mark

The diagram shows the structures of three substances that have giant covalent structures.

Three labelled lattice diagrams. Diamond is drawn as a three-dimensional network in which every carbon atom is joined to four others. Graphite is drawn as two flat layers of linked hexagonal rings stacked one above the other. Silicon dioxide is drawn as a three-dimensional network of two kinds of atom, with a key showing that the larger black circles are silicon and the smaller grey circles are oxygen.

Which does not provide the correct explanation of the property of a substance?

Substance

Property

Explanation

A

graphite

conducts electricity

its ions are free to move through the layers

B

diamond

hard

each carbon atom is covalently bonded to four other carbon atoms

C

silicon dioxide

high melting point

it has many strong covalent bonds which require a large amount of energy to break

D

graphite

soft

its layers can slide over each other

    Choose your answer

    2a
    1 mark

    Which best describes a covalent bond?

    • Sea of delocalised electrons and positive metal ions

    • Attraction between positive and negative ions

    • Shared pair of electrons between two non-metal atoms

    • Weak intermolecular forces 

    Choose your answer

    2b
    1 mark

    Which of the following substances will bond covalently?

    • Sodium oxide

    • Sodium

    • Sodium bromide

    • Oxygen

    Choose your answer

    2c
    1 mark

    Hydrogen is an atom which has one electron in the outermost shell. Complete the dot-and-cross diagram to show the bonding in a hydrogen molecule.

    An incomplete dot-and-cross diagram for a hydrogen molecule. Two circles overlap, each labelled H, and no electrons are drawn on either of them.

    How did you do?

    2d
    1 mark

    Hydrogen is a gas at room temperature.

    Why is hydrogen a gas at room temperature?

    • The intermolecular forces are strong

    • The bonding in hydrogen is weak

    • The intermolecular forces are weak

    Choose your answer

    3a
    3 marks

    This question is about allotropes of carbon. Match the name of the substance to its structure. You must only draw one line from each substance.

    Three named boxes down the left-hand side, reading from top to bottom Diamond, C60 fullerene and Graphite, each with a dot on its right-hand edge. Three boxed structure diagrams down the right-hand side, each with a dot on its left-hand edge. The top diagram is a three-dimensional lattice of dark spheres joined by straight bonds into linked rings. The middle diagram is three flat sheets of joined rings stacked one above another with a gap between the sheets. The bottom diagram is a hollow ball made of pale spheres joined into rings covering its surface. No lines are drawn between the two sides.

    How did you do?

    3b
    1 mark

    What type of bonding is found in the structures in part (a)?

    • Ionic

    • Covalent

    • Metallic

    Choose your answer

    3c
    1 mark

    Which substance conducts electricity?

    • Diamond

    • C60 fullerene

    • Graphite

    Choose your answer

    3d
    2 marks

    Complete the sentence to describe and explain the melting points of diamond and graphite. 

    Their melting points are ____________________ due to strong covalent bonds needing lots of ___________________ to break. 

    How did you do?

    4a
    2 marks

    Hydrogen and carbon atoms form the hydrocarbon molecule methane.

    The diagram in Figure 1 shows how the outer electrons are arranged in an atom of hydrogen and carbon.

    Two circles side by side. The one labelled C carries four dots spaced around it, and the one labelled H carries a single cross.

    Figure 1

    Complete Figure 2 to show how the outer electrons are arranged in a molecule of methane (CH4).

    An incomplete diagram for methane. A central circle labelled C is overlapped by four circles labelled H, one above, one below, one to the left and one to the right. No electrons are drawn in any of the overlaps.

    Figure 2

    How did you do?

    4b
    1 mark

    What is the type of bond in a molecule of methane?

    • Metallic

    • Ionic

    • Covalent

    Choose your answer

    4c
    3 marks

    Methane has a boiling point of -162 °C. At room temperature it is a gas.

    Explain why methane is a gas at room temperature.

    How did you do?

    4d
    1 mark

    Methane is a simple molecule and it does not conduct electricity.

    Which statement is the correct reason for this?

    • Electrons are fixed in position

    • The ions are free to move and carry a charge

    • There are no free electrons to carry the charge

    • The bonds contain no electrons

    Choose your answer

    5a
    1 mark

    The alkanes are a family of hydrocarbons with the general formula CnH2n+2. Ethane, C2H6, and butane, C4H10, are examples of alkanes. 

    Ethane has a boiling point of -89 °C and butane has a higher boiling point of -1 °C.

    Why is the boiling point of butane higher than ethane?

    • Butane is ionically bonded

    • Butane has a higher Mr than ethane

    • Butane has stronger bonds between the carbon and hydrogen atoms

    • Ethane has a higher Mr than butane

    Choose your answer

    5b
    3 marks

    Complete the sentences below using words from the box.

    conduct               atoms              free                 shells

    fixed                      insulate                     ions                    electrons

    Ethane and butane do not ________________ electricity because there are no ________________ ions / _______________ that are able to move and carry charge. 

    How did you do?

    5c
    1 mark

    What is the type of bonding in ethane and butane?

    How did you do?

    5d
    1 mark

    Ethane and butane only contain single bonds. Double bonds can also form between a different family of hydrocarbons called alkenes. Which of the following statements is correct?

    • A double bond contains two electrons

    • A double bond contains two pairs of electrons

    Choose your answer

    1a
    2 marks

    Halon 1301 is a compound used in some fire extinguishers.

    Halon 1301 has the percentage composition by mass of

    C 8.05%   Br 53.69%   F 38.26%

    Show, by calculation, that the empirical formula of this compound is CBrF3 

    How did you do?

    1b
    2 marks

    The diagram shows the displayed formula of a molecule of Halon 1301.

    A displayed formula. A central carbon atom is joined by single bonds to a bromine atom on its left, a fluorine atom above, a fluorine atom to its right and a fluorine atom below.

    Draw a dot-and-cross diagram to show all the outer electrons in this molecule.

    How did you do?

    1c
    2 marks

    The boiling point of Halon 1301 is −58 °C.

    Explain why Halon 1301 has a low boiling point.

    How did you do?

    2a
    2 marks

    Diamond, graphite and silicon dioxide all have giant covalent structures.

    The diagram shows the structures of these three substances.

    Three labelled lattice diagrams. Diamond is drawn as a three-dimensional network in which every carbon atom is joined to four others. Graphite is drawn as two flat layers of linked hexagonal rings stacked one above the other. Silicon dioxide is drawn as a three-dimensional network of two kinds of atom, with a key showing that the larger dark circles are silicon and the smaller grey circles are oxygen.

    Explain why silicon dioxide has a high melting point.

    How did you do?

    2b
    2 marks

    Explain why graphite conducts electricity. 

    How did you do?

    2c
    2 marks

    State why diamond is hard but graphite is soft.

    How did you do?

    3a
    3 marks

    Carbon dioxide changes directly from a solid to a gas without becoming a liquid.

    i) Give the name of the change of state from solid to gas.

    [1]

    ii) Describe the test for carbon dioxide gas.

    [2]

    How did you do?

    3b
    2 marks

    Carbon dioxide is a simple molecular covalent substance. Explain why carbon dioxide turns from a solid to a gas at a very low temperature.

    How did you do?

    3c
    6 marks

    Diamond and graphite are both giant covalent substances made up of carbon atoms.

    • diamonds are used in cutting tools

    • graphite is used in pencils to make marks on paper

    Explain, with reference to structure and bonding, why each substance is suitable for its particular use.

    How did you do?

    4a
    3 marks

    Chlorine, bromine and iodine are elements in the Periodic Table.

    Explain how the position of these elements in the Periodic Table depends on their electronic configurations.

    How did you do?

    4b
    8 marks

    Chlorine reacts with methane to form CH3Cl and HCl

    i) State the condition necessary for this reaction.

    [1]

    ii) Give the equation for this reaction.

    [1]

    iii) The bonds in a molecule of CH3Cl are covalent.

    Explain, in terms of electrostatic attractions, what is meant by a covalent bond.

    [2]

    iv) Draw a dot‐and‐cross diagram for a molecule of CH3Cl

    Show only the outer electrons of the atoms.

    [2]

    An outline for a dot-and-cross diagram of chloromethane, with no circles and no electrons drawn. A letter C stands in the centre, with an H above it, an H below it, an H to its left and Cl to its right.

    v) CH3Cl has a simple molecular structure.

    Explain why CH3Cl has a low boiling point.

    [2]

    How did you do?

    4c
    2 marks

    Graphite is another substance that contains covalent bonds.

    The diagram shows the structure of graphite.

    A structure diagram of graphite. Two flat layers of linked hexagonal rings of carbon atoms are stacked one above the other, with a gap between the layers.

    Most covalent substances do not conduct electricity.

    Explain why graphite is able to conduct electricity.

    [2]

    How did you do?

    5
    1 mark

    Carbon dioxide contains covalent bonds.

    The covalent bonds in a molecule of carbon dioxide can be represented by a dot-and-cross diagram.

    Which is the correct dot-and-cross diagram for carbon dioxide?

    • A dot-and-cross diagram for carbon dioxide. A central carbon circle overlaps an oxygen circle on each side. Each overlap holds two dots and two crosses, making a double bond, and each oxygen carries four further dots on the rest of its shell.
    • A dot-and-cross diagram for carbon dioxide. A central carbon circle overlaps an oxygen circle on each side. Each overlap holds only one dot and one cross, making a single bond, the carbon carries a cross above and below outside the overlaps, and each oxygen carries six further dots on the rest of its shell.
    • A dot-and-cross diagram for carbon dioxide. A central carbon circle overlaps an oxygen circle on each side. Each overlap holds two dots but no crosses, and the carbon carries two crosses above and two below outside the overlaps.
    • A dot-and-cross diagram for carbon dioxide. A central carbon circle overlaps an oxygen circle on each side. Each overlap holds two dots and two crosses, making a double bond, but each oxygen carries six further dots on the rest of its shell rather than four.

    Choose your answer

    6a
    3 marks

    Diamond is a naturally‐occurring form of carbon. It has a giant molecular structure. Explain, with reference to its structure and bonding, why diamond has a high melting point.

    How did you do?

    6b
    3 marks

    C60 fullerene is another form of carbon. The diagram shows a molecule of C60 fullerene.

    A molecule of C~60~ fullerene, drawn as a hollow ball of carbon atoms joined into five- and six-membered rings over its surface.

    i) Explain why C60 fullerene has a much lower melting point than diamond.

    [2]

    ii) C60 fullerene is used by doctors when injecting medicines into their patients. C60 fullerene allows medicines, which might damage some parts of the body, to reach the part of the body where they are needed.

    Suggest why C60 fullerene is suitable for this purpose.

    [1]

    How did you do?

    6c
    5 marks

    Graphite is another naturally‐occurring form of carbon. Graphite can be used in pencils because it is soft and can leave marks on paper. Graphite can also be used as a conductor of electricity. Explain why graphite is soft and conducts electricity. Refer to structure and bonding in your answer.

    How did you do?

    7a
    4 marks

    This question is about carbon and its compounds.

    i) Draw a dot-and-cross diagram to show the outer shell electrons in a molecule of carbon dioxide, CO2.

    [2]

    ii) The atoms in carbon dioxide are held together by covalent bonds. Describe the forces of attraction in a covalent bond.

    [2]

    How did you do?

    7b
    7 marks

    The diagram shows three different structures of carbon.

    Three labelled structures. Diamond is drawn as a three-dimensional network in which every carbon atom is joined to four others. Graphite is drawn as three flat layers of linked hexagonal rings stacked one above another with gaps between them. C~60~ fullerene is drawn as a hollow ball of carbon atoms joined into rings over its surface.

    i) Explain why graphite conducts electricity.

    [2]

    ii) Explain why diamond has a much higher melting point than C60 fullerene. Refer to structure and bonding in your answer.

    [5]

    How did you do?

    8
    1 mark

    Silicon dioxide, SiO2, and silicon(IV) chloride, SiCl4, are both covalently bonded compounds.

    The table below shows the melting point and boiling point of these compounds.

    Compound

    Melting point / o C

    Boiling point / o C

    Silicon dioxide

    1710

    2230

    Silicon(IV) chloride

    -69

    58

    Which statement is not correct about the two compounds?

    • at room temperature silicon dioxide is a solid and silicon(IV) chloride is a liquid

    • silicon dioxide has a giant covalent structure

    • silicon(IV) chloride has a lower melting point as it has fewer covalent bonds to overcome

    • silicon(IV) chloride has a simple molecular structure

    Choose your answer

    9
    1 mark

    Ammonia, NH3, is a small covalent molecule.

    How many non-bonding, outer-shell electrons are present in one molecule of ammonia?

    • 0

    • 2

    • 5

    • 6

    Choose your answer

    1a
    4 marks

    This question is about substances with covalent bonds.

    i) Draw a dot and cross diagram to show the outer shell electrons in a molecule of nitrogen, N2

    [2]

    An outline for a dot-and-cross diagram of a diatomic molecule. Two large circles overlap, each with only a single dot at its centre marking the nucleus, and no electrons drawn on either shell.

    ii) Describe the forces of attraction in a covalent bond.

    [2]

    How did you do?

    1b
    5 marks

    The diagram shows three different structures of carbon.

    A three-dimensional network in which every carbon atom is joined to four others.
    Three flat layers of linked hexagonal rings of carbon atoms, stacked one above another with gaps between the layers.
    A hollow ball of carbon atoms joined into rings over its surface.

    Structure A

    Graphite

    C60 Fullerene

    i) Name structure A.

    [1]

    ii) Graphite and C60 fullerene contain covalent bonds, but have different structures.

    Explain why C60 fullerene has a much lower melting point than graphite.

    Refer to structure and bonding in your answer.

    [4]

    How did you do?

    2a
    1 mark

    This question is about some compounds of the elements in Group 4 of the Periodic Table.

    When carbon dioxide dissolves in water, a weak acid forms.

    Which of these could be the pH of this weak acid?

    • 1

    • 5

    • 7

    • 9

    Choose your answer

    2b
    1 mark

    Which of these is a correct statement about acids?

    • acids contain OH− ions

    • acids are electron donors

    • acids are proton acceptors

    • acids are proton donors

    Choose your answer

    2c
    2 marks

    When lead(II) carbonate is heated, lead(II) oxide and carbon dioxide form.

    i) Give the name of this type of reaction.

    [1]

    ii) Complete the equation for this reaction.

    [1]

    PbCO3 → .............................................. + ..............................................

    How did you do?

    2d
    7 marks

    Silicon dioxide, SiO2, and silicon(IV) chloride, SiCl4, are both covalently bonded compounds. The table shows the melting and boiling points of these two compounds, and the physical state of silicon dioxide at room temperature.

    Compound

    Melting point in °C

    Boiling point in °C

    Physical state at room temperature

    SiO2

    1710

    2230

    solid

    SiCl4

    −69

    58

    i) Complete the table by giving the physical state of silicon(IV) chloride at room temperature.

    [1]

    ii) Explain, in terms of structure and bonding, why silicon dioxide has a much higher melting point than silicon(IV) chloride.

    [6]

    How did you do?

    3a
    1 mark

    This question is about covalent bonding.

    What is a covalent bond? 

    How did you do?

    3b
    1 mark

    Complete the dot and cross diagram to show the bonding in propane.

    An incomplete dot-and-cross diagram for propane. Three circles labelled C sit in a row, each overlapping its neighbour. The first and third carbons are each overlapped by three circles labelled H and the middle carbon by two, and no electrons are drawn in any of the overlaps.

    [1]

    How did you do?

    3c
    2 marks

    Explain why propane cannot conduct electricity. 

    How did you do?

    3d
    2 marks

    Carbon dioxide, CO2, bonds in a similar way to propane. Complete the diagram to show the bonding.

    An incomplete dot-and-cross diagram for carbon dioxide. A circle labelled C sits between two circles labelled O, each overlapping the central one, and no electrons are drawn anywhere.

    How did you do?

    4a
    2 marks

    This question is about the properties and bonding in allotropes of carbon.

    Substance X is an allotrope of carbon and has the following properties and uses:

    • It is strong

    • It is a good conductor of electricity

    • It is used to overlay monitor screens to make them touchscreen

    Identify substance X.

    Explain your answer.

    How did you do?

    4b
    2 marks

    Buckminsterfullerene is another allotrope of carbon.

    Explain why this substance can be used as a lubricant. 

    How did you do?

    4c
    3 marks

    Fullerenes are also used as catalysts and in electronics.

    Suggest why they can each be used for these applications.

        catalysts:

       electronics:

    How did you do?

    4d
    2 marks

    Explain how a catalyst increases the rate of a reaction. 

    How did you do?