Covalent Bonding (Edexcel IGCSE Science (Double Award): Chemistry)

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.

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)

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?

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)

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

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

Ammonia, NH₃, is a small covalent molecule.

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