2.2 Bonding & Substance Properties

This question is about the bonding and structure of silicon dioxide. 

Figure 1 shows the structure of part of silicon dioxide. 

Figure 1

Explain why silicon dioxide can be used to line furnaces. 

Explain why silicon dioxide cannot conduct electricity.

Silicon dioxide is a solid at room temperature. 

Solids can be represented using the particle model in Figure 2. 

Figure 2

Describe two limitations of this model.

Explain how, using particle theory, silicon dioxide would change state from a solid to a liquid. 

This question is about the structure and bonding in ethene. 

Ethene belongs to the homologous series of alkenes and has the formula  C₂H₄.

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

Only show the outer shell electrons.

Figure 1

Table 1 shows information on the boiling points and structures of ethene and two other alkenes.

Table 1 

Name	Ethene	Propene	Butene
Structure
Boiling Point in oC	-104	-47	-6.3

Use your knowledge of structure and bonding to describe and explain the trend in boiling point as the number of carbon atoms increases. 

Ethene can undergo addition polymerisation to form the polymer poly(ethene). 

Why is poly(ethene) a solid at room temperature? 

Complete the structure for poly(ethene) in Figure 2. 

Figure 2

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. 

This question is about metals and alloys.

Stainless steel is an alloy of iron, chromium and nickel. 

Iron is a typical metal.

Explain why it has a high melting point.

Explain why stainless steel is harder than the iron it is made from. 

Explain why nickel and chromium are both good thermal conductors.

A student was investigating a calcium salt labelled Y.

The student found that Y:

• has a very high melting point
• does not conduct electricity
• is water soluble and the solution produced conducts electricity

What type of bonding is present in salt Y?

Explain why the solid Y does not conduct electricity but its aqueous solution does.

Figure 1 shows the bonding arrangement of an element. 

Figure 1

What is the element? 

Tick (✔) one box.

The image in Figure 1 is an allotrope. 

Why does this allotrope conduct electricity? 

Figure 2 shows the particle diagram of an alloy. 

Figure 2

Explain why this alloy is harder than pure metal Y.

What kind of substances are alloys?

Tick (✔) one box.

The hydrogen halides (HF, HCl, HBr and HI) are compounds used to produce acids.

Figure 1 represents a molecule of hydrogen chloride.

Figure 1

What do the crosses (X) represent?

What type of bonding is present in this molecule?

Predict whether hydrogen chloride is a solid, liquid or gas at room temperature and pressure. 

Explain your answer.

This question is based on the chemistry of polymers.

Polyvinyl chloride (PVC) is a commonly used polymer.

State the term used to describe the units from which polymers are made and name the type of bonding between these units.

Figure 1 represents short chains of PVC.

Figure 1

Although hard material is used in water pipes and drains, PVC softens and melts when heated. 

Use the diagram and your knowledge of structure and bonding to explain why this occurs.

The basic unit of polyvinyl chloride is C₂H₃Cl.

The polymer chain consists of many of these base units bonded together.

In the space provided, draw a section of a chain of PVC showing three units joined together.

Marble slabs for kitchen countertops are cut from huge blocks of marble which are extracted from quarries. The extraction process involves cutting the marble blocks with a metal cable connected to a rotary motor. Water is sprayed onto the marble for cooling.

The cable used is made from a steel alloy. 

Suggest two advantages of using an alloy instead of a pure metal for this process.

For particularly dense marble, or marble which contains grains of other rock types, the cutting cable is encrusted with diamond dust.

Suggest a reason why.

Diamond has a very high melting points.

Explain why in terms of the bonding arrangement.

Explain why diamond has a higher melting and boiling point than carbon dioxide.

Metals are good conductors of electricity. 

Explain why.