Bonding, Structure & Properties (WJEC GCSE Chemistry)

The table shows the electronic structure of the elements present in potassium fluoride. 

The diagram shows the electron transfer that occurs when potassium reacts with fluorine to form potassium fluoride. The • and × symbols are outer shell electrons.

A student was asked to draw a diagram showing the electronic structures and charges on the ions formed. There are two mistakes in the student’s answer.

i) Circle the two mistakes in the student’s answer.

[2]

ii) Name the type of bonding found in potassium fluoride.

[1]

iii) The diagrams show four different structures. Give the letter of the structure most likely to represent potassium fluoride.

[1]

Letter ...........................

The diagram shows the electrons in the outer shell of an atom of fluorine.

Complete the diagram to show the outer shell electrons in a molecule of fluorine.

Scientists make ‘new fuel’ discovery

Methanol is vital in manufacturing a wide range of fuels and chemicals. Methanol is produced from methane found in natural gas. At the moment methane is condensed into liquid natural gas at the site where it is extracted and transported in pressurised containers.

Traditionally, methanol is created by converting methane into hydrogen and carbon monoxide molecules at high temperature, then rearranging the atoms in a different order in a second highly pressurised process. The current two-stage process is very energy intensive, as it burns a lot of fossil fuel to achieve high temperatures.

Scientists have discovered a new way of creating greener and cheaper methanol from methane using gold palladium nano-particles to initiate a one-stage chemical reaction that can be done at temperatures no higher than 50°C. In this new process the gold palladium nanoparticles act as a catalyst enabling methane and oxygen to combine, forming methanol in a single stage reaction. 

The discovery opens up the prospect of easily converting methane into methanol at the site where the methane is extracted, so that methanol can be transported as a liquid at atmospheric pressure.

Nano-particles have very different and unique properties from their bulk form.

Tick (✓) the box next to the two statements which support the opinion that the new method is more environmentally friendly.

Complete the balanced equation for the new method of converting methane to methanol.

2CH₄ +    .......................   ........................

Tick (✓) the box next to the true statement.

The table shows the electronic structure of the elements present in water.

The diagrams show the outer shell electrons in an atom of hydrogen and an atom of oxygen.

i) Complete the diagram to show the outer shell electrons in a molecule of water.

[2]

ii) The diagram shows some water molecules and the weak forces between them. 

Put a tick (✓) in the box next to the property of water which can be explained by the weak forces between water molecules.

[1]

The diagram shows the apparatus used by a group of students to investigate the volume of hydrogen and oxygen gas formed during the electrolysis of water.

The overall equation for the electrolysis of water is as follows.

2H₂O  2H₂ + O₂

i) The table shows the total volume of hydrogen formed over 10 minutes.

I. Plot the values from the table on the grid. Draw a suitable line. Label this line ‘hydrogen’.

   (0,0) has been plotted for you.

[2]

II. Using a ruler, draw a second line on the grid to show the volume of oxygen that would be collected during the same 10 minutes. Label this line ‘oxygen’.

[1]

III. Describe the relationship between the volume of hydrogen and the volume of oxygen formed during electrolysis.

[2]

ii) Electrolysis of water can be represented by the following equation.

2H₂O  2H₂ + O₂

Give the letter, A, B, C or D, of the diagram which also represents this reaction.

[1]

Letter ..........................................

One use of electrolysis is in electroplating. The diagram shows the silver plating of a metal spoon.

i) State why this process does not work for a plastic spoon.

[1]

ii) Explain why the silver ions move towards the spoon.

[2]

iii) Put a tick (✓) in the box next to the electrode equation for the reaction at electrode B.

[1]

Smart materials are used to make the frames and lenses of certain spectacles.

Give the names of the different types of smart material used. Describe the unusual property of each.

Frames .......................................................................................

Lenses .......................................................................................

Higher Tier Only

Titanium dioxide has been used in sun creams for decades. Sun screens available today use nano-scale titanium dioxide particles. Some people believe using creams containing nano-particles is unsafe.

i) Give the advantage of using nano-scale titanium dioxide particles rather than larger titanium dioxide particles to make sun screens.

[1]

ii) Explain why some people are concerned about the use of nano-scale titanium dioxide particles in sun screens.

[2]

iii) Approximately how many times bigger are common titanium dioxide particles (3 × 10^–7 m) than nano-scale titanium dioxide particles (2.5 × 10^–10 m)?

[2]

Calcium and oxygen react forming calcium oxide.

i) Explain, using dot and cross diagrams, how bonding takes place during the formation of calcium oxide. 

[2]

ii)

Explain why both of these compounds have high melting points and why the melting point of calcium oxide is higher.

[2]

Graphene and graphite are different forms of carbon.

i) Explain how the bonding present in both forms makes them good conductors of electricity.

[2]

ii) Carbon nanotubes can be formed by rolling up graphene sheets.

A sheet of graphene 11 unit cells in width was rolled up to form a nanotube. Use the information below to calculate the diameter, in metres, of the nanotube formed. Write your answer in standard form. 

[3]

circumference = π × diameter
π = 3.14
1 nm = 1 × 10⁻⁹ m

Diameter = ............................. m

Silver can be recovered from photographic solutions using iron. This reaction can be demonstrated in the laboratory by adding iron filings to a beaker containing silver nitrate solution. A grey solid forms and the solution turns a pale green colour.

Explain the reaction taking place in the beaker.

Higher Tier Only

Nano-silver has become widely used in everyday life. Explain one disadvantage of using nano-silver in sports clothing.

Describe what is meant by a smart material. Use thermochromic and photochromic materials to support your answer, giving everyday uses of each.

The following table contains some information about five elements, A, B, C, D and E.

Give the letter of the element, A-E, that is a liquid at 20 °C. Explain your choice.

State which element could be iron and explain your choice.

State one property of iron that is not mentioned in the table.

Draw a line from each type of structure to its property. One has been done for you.

Smart materials have properties which change reversibly with a change in their surroundings. The box below shows the names of some smart materials.

From the box above, choose the smart material used in making each of the following items.

Lithium chloride is a solid with a high melting point. It conducts electricity only when molten or in solution.

Describe the bonding present in lithium chloride and explain the properties given above.

Li = 2,1                Cl = 2,8,7

You may include a diagram in your answer.

Seawater is an important raw material from which many different substances can be obtained.

The table below shows the concentration (measured in g / kg of seawater) of the most abundant ions found in seawater.

Use the information in the table to answer the following questions.

i) Name the two most abundant ions in seawater.

[1]

ii) Give the chemical formula of the compound formed from these ions.

[1]

Both chlorine and iodine were once obtained from seawater.

Suggest why it is too expensive to use seawater as a source of iodine.

The table below shows some properties of three elements in the Periodic Table.

Describe how the information in the table shows that silicon is difficult to classify as a metal or a non-metal.

Give the symbol of the element which is found in Group 2 and Period 3 of the Periodic Table.

i) The chemical formula of copper(II) nitrate is Cu(NO₃)₂.

Give the number of nitrogen atoms in the formula Cu(NO₃)₂.

[1]

ii) Give the chemical formula of silver oxide.

[1]

Higher Tier Only

Nano-scale silver particles are added to socks to reduce the effects of smelly feet. Recent research has found that these particles can easily leak into waste water during washing.

i) State the property of nano-scale silver particles that makes them useful in socks.

[1]

ii) Suggest a reason why some scientists are concerned about nano-scale silver particles entering waste water.

[1]

The following boxes show some information about the structures of diamond and graphite.

Each carbon atom is bonded strongly to four others. All four outer electrons are used in bonding.	Each carbon atom is bonded strongly to three others. They form layers that are held together weakly. Three electrons are involved in bonding whilst the other moves freely between the layers.

State why both substances have high melting points.

State which of the above substances will conduct electricity. Give a reason for your answer. 

Substance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Explanation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Graphite is used in pencils. Explain in terms of structure why this is possible.

Using water and carbon dioxide as examples, explain what is meant by covalent bonding and why some molecules contain double bonds. You may use diagrams as part of your answer.

Covalent bonds are formed by the sharing of pairs of electrons.

The following diagrams show the structures of hydrogen and diamond, a form of carbon.

Explain why diamond has a higher melting point than hydrogen.

Graphite is another form of carbon that has a high melting point. Give one other property of graphite and explain this property in terms of structure and bonding.

The bonding in oxygen, O₂, is also covalent. Draw a dot and cross diagram to show the bonding present in a molecule of oxygen.

O = 2,6

This question is about nanoparticles in products used for protection against the sun.

Explain why nanoparticles of titanium oxide are able to pass through the skin and travel around the body more easily than normal-sized particles of the same compound.

Give three reasons why sunscreens containing nanoparticles should be subjected to further testing.

Suggest why some companies that make sun creams might prefer to not engage in further testing.

Graphene is a single layer of graphite.

It can conduct electricity and can be used in loudspeakers.

Explain why graphene can conduct electricity. 

Explain why graphene is strong.

Explain why graphite can be used in the tips of pencils. 

This question is about the bonding and structure of diamond.

State two uses of diamonds.

Figure 1 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.

Figure 1

Explain why diamond has a high melting point.

This question is about fullerenes.

Fullerenes can form nanotubes which consist of tiny carbon cylinders.

A carbon nanotube is shown in Figure 1.

Figure 1

Explain the properties of carbon nanotubes.

Answer in terms of structure and bonding.

Carbon can react with oxygen to form carbon dioxide.

Complete the dot and cross diagram in Figure 2 to show the bonding in this molecule.

Show the outer electrons only. 

Figure 2

Explain why carbon dioxide cannot conduct electricity.

This question is about sodium chloride and diamond.

Figure 1 shows the structure of sodium chloride and diamond. 

Figure 1 

Sodium chloride has a melting point of 801^oC. 

Explain why sodium chloride has a high melting point.

Diamond has a melting point of 4500 ^oC.

Explain why diamond has a higher melting point than sodium chloride.

Refer to the structure of diamond in your answer. 

Compare the electrical conductivity of sodium chloride and diamond.

Explain your answer.