Covalent bonding (Edexcel IGCSE Chemistry (Modular): Unit 2)

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 

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

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

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

 Explain why Halon 1301 has a low boiling point.

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

The diagram shows the structures of these three substances.

Explain why silicon dioxide has a high melting point.

Explain why graphite conducts electricity. 

State why diamond is hard but graphite is soft.

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)

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

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.

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.

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)

 v) CH₃Cl has a simple molecular structure.

 Explain why CH₃Cl has a low boiling point.

 (2)

Graphite is another substance that contains covalent bonds.

 The diagram shows the structure of graphite.

 Most covalent substances do not conduct electricity. 

Explain why graphite is able to conduct electricity.

 (2)

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?

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.

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

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)

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.

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)

The diagram shows three different structures of carbon.

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)

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.

Which statement is not correct about the two compounds?

Ammonia, NH₃, is a small covalent molecule.

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

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)

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

 (2)

The diagram shows three different structures of carbon.

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)

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.

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

(1)

ii) Which of these is a correct statement about acids?

(1)

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 → .............................................. + ..............................................

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.

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)

This question is about covalent bonding.

What is a covalent bond? 

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

(1) 

Explain why propane cannot conduct electricity. 

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

This question is about the bonding and structure of diamond.

State two uses of diamonds.

The diagram shows the outer electron shells of carbon atoms in a lattice structure of diamond.

Using dots, add electrons to the diagram to represent the bonding arrangement.

Explain why diamond has a high melting point. 

The type of bonding in ethene gas, C₂H₄, is the same type of bonding that occurs in diamond. Explain why ethene is a gas at room temperature.

The boiling point of other molecules in the same family as ethene are shown below.

State and explain the trend in the boiling point. 

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 or electricity

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

Identify substance X.

Explain your answer.     

Buckminsterfullerene is another allotrope of carbon.

Explain why this substance can be used as a lubricant. 

Fullerenes are also used as catalysts and in electronics.

Suggest why they can each be used for these applications.

    catalysts: ____________________________________________ 

   electronics: ___________________________________________

Explain how a catalyst increases the rate of a reaction.