Covalent Bonding (Edexcel GCSE Chemistry): Exam Questions

Ammonia, NH₃, is a small covalent molecule.

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

Covalent substances can be simple molecular covalent or giant covalent.

i) Ammonia is a simple molecular, covalent substance. Which is the most likely set of properties for ammonia?

(1)      

ii) Ammonia, NH₃, is made by reacting nitrogen with hydrogen. Write the balanced equation for this reaction.

(2)

Oxygen, O₂, is also a simple molecular, covalent substance.

Draw a dot and cross diagram for the molecule of oxygen.

Figure 8 shows the arrangement of carbon atoms in diamond, graphene and a fullerene (C₆₀).

Figure 8

Consider these three substances.

Explain, in terms of their structures and bonding, their relative melting points, strengths and abilities to conduct electricity.

Which statement is not true about covalent bonding? 

What are the typical sizes, in orders of magnitude, of atoms and small molecules? 

Iodine and bromine are both halogens. The bonding in iodine is similar to the bonding in bromine.

Suggest two reasons why they bond in similar ways.

Complete the diagram below to show the bonding arrangement in a molecule of iodine.

Show the outer shell electrons only.

Explain why liquid iodine is unable to conduct electricity.

Iodine has an atomic number of 53 and xenon has an atomic number of 54. Explain why xenon exists as an atom where as iodine exists as a molecule.

An oxygen molecule, O₂, is formed when two oxygen atoms covalently bond together.

How many electrons need to be shared between these two oxygen atoms?

Hydrogen, carbon, oxygen and chlorine can all form covalent bonds by sharing electrons.

How many electrons does each element need to share in order to complete its outer shell?

Figure 1 shows the displayed structure of ethanol 

Complete the dot and cross diagram in Figure 2 to show the bonding in ethanol. Show the outer shell electrons only.

Ethanol has a boiling point of 79 °C. Explain why ethanol has a low boiling point.

Explain, in terms of particles, why ethanol does not conduct electricity.

Methane and water are both simple molecules containing covalent bonds.

Which statement is not correct?

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?

Sulfur can form covalent bonds.

Complete the dot and cross diagram in Figure 1 to show the covalent bonding in a molecule of hydrogen sulfide.

Show the outer shell electrons only.

Which of the following set of properties is most likely to be hydrogen sulfide?

The atoms in carbon dioxide are held together by covalent bonds.

Describe the forces of attraction in a covalent bond.

This question is about covalent bonding.

What is a covalent bond? 

Complete the dot and cross diagram in Figure 1 to show the bonding in propane. 

Figure 1

Explain why propane cannot conduct electricity. 

Carbon dioxide, CO₂, bonds in a similar way to propane. Complete Figure 2 to show the bonding.

Figure 2

A hydrogen atom is 0.074 nm, or 0.00000000074 m long.

Write 0.00000000074 m in standard form.

Caesium atoms are 0.267 nm long.

State how many orders of magnitude exist between the length of a hydrogen atom and the length of a caesium atom.

Hydrogen exists as molecules.

Draw a dot-cross diagram for a hydrogen molecule.

Hydrogen molecules are the smallest molecules.

Explain why.

Figure 1 shows a dot-cross diagram and structure of a methane molecule.

                                             Dot-cross diagram                                                                      Structure

Figure 1

Name the type of bond formed when two atoms share a pair of electrons.

Complete Figure 2 to show the dot cross diagram of a carbon dioxide molecule.

Figure 2

Draw the structure of a carbon dioxide molecule.

The boiling point of methane is -162°C. The boiling point of carbon dioxide is -75°C.

A student concludes that this difference is due to the number of bonds between the atoms in each molecule.

Discuss if you think this conclusion is correct.

An ethene molecule contains carbon and hydrogen atoms. Its formula is C₂H₄.

Complete the dot and cross diagram of ethene, shown in Figure 1.

Figure 1

Complete Figure 2 to show the structure of ethene.

Use a single line to show each covalent bond.

Figure 2

Give an advantage of using Figure 1 rather than Figure 2 to represent ethene.

Higher Tier Only

Table 1 shows the bond energies for a single and double carbon bond.

Table 1

Describe and explain the difference between the bond energies.

A nitrogen molecule has the formula N₂.

Nitrogen molecules are diatomic. Suggest what this means.

Nitrogen atoms have the electronic configuration 2.8.5.

Draw a dot and cross diagram to show the covalent bonding in a nitrogen molecule.

Show only the electrons in the outer shell.

Use your knowledge of bonding to explain why nitrogen is a gas at room temperature.

Nitrogen is an unreactive gas.

Suggest why.

Diamond is made up of carbon atoms.

Figure 1 shows the structure of diamond.

The black dots represent the carbon atoms.

The lines represent bonds.

Figure 1

Name the type of bonding in diamond.

Explain why each carbon atom forms four bonds.

Carbon can also form compounds like methane (CH₄).

Draw a dot and cross diagram to show the bonding in methane.

Show the outer electrons only.

The melting point of diamond is around 4500°C.

The melting point of methane is -182°C.

Explain this difference using your knowledge of bonding.

Ethanoic acid is the acid found in vinegar.

Figure 1 shows the dot and cross structure of ethanoic acid.

Figure 1

State what each dot and cross represents.

Complete Figure 2 to show the structure of an ethanoic acid molecule.

Use a single line to show each bond.

Figure 2

Determine the empirical formula of ethanoic acid.

The boiling point of ethanoic acid is 118°C.

The boiling point of water is 100°C.

Use your knowledge of bonding to suggest a reason for the difference.

An atom has a length of 0.1 nm.
A grain of sand has a length of 1 mm.
1 mm = 1 million nm

Calculate how many atoms could line up next to each other on a grain of sand.

Calculate the order of magnitude between the length of an atom and a grain of sand.

Atoms bond together to form molecules.

Show the bonding in a chlorine molecule. Only include the electrons in the outer shell.

Chlorine is found in Group 7 of the Periodic Table. All elements in Group 7 form molecules with two atoms.

Explain how the size of the molecule changes as you go down Group 7.

Figure 1 shows the structure of hydrogen peroxide.

Figure 1

The lines represent covalent bonds.

Explain why hydrogen peroxide contains covalent, not ionic bonds.

Calculate the relative formula mass of hydrogen peroxide.

(M_r H = 1, M_r O = 16)

Complete Figure 2 to show the dot and cross diagram for hydrogen peroxide.

Figure 2

A student said ‘Covalent bonds only exist between atoms of different elements’.

Use an example to show that this statement is incorrect.

This question is about trends in the sizes of atoms.

Group 0 of the Periodic table contains the noble gases.

i) Predict how the size of the atoms changes as you go down Group 0.

 [1]

ii) Explain your answer to part i)

[1]

Figure 1 is a graph that shows how the length of atoms changes as you go across Period 3 of the Periodic Table.

Figure 1

i) Describe what the graph shows.

[1]

ii) Suggest a reason for this trend.

[3]

Group 7 contains the halogens.

Hydrogen reacts with halogens to form simple covalent molecules called hydrogen halides.

Draw a dot cross diagram to show the bonding in the molecule formed when hydrogen reacts with chlorine

Higher Tier Only

Figure 2 shows the bond energies in hydrogen halides.

Figure 2

Suggest an explanation for the trend shown in Figure 2.