2.4 Giant Structures

Extended Only 

It was reported from America that a turbine engine, the size of a button, might replace batteries. The engine would be built  from silicon which has suitable properties for this purpose.

The engine will run on a small pack of jet fuel. What other chemical is needed to burn this fuel?

Extended Only 

Silicon has the same type of macromolecular structure as diamond.

[2]

[2]

[1]

Separate: Chemistry and Extended Only

Silicon is made by the carbon reduction of the macromolecular compound, silicon(IV) oxide.

SiO₂ + .......... C + → Si + ..........CO

[1]

There are three types of giant structure – ionic, metallic and macromolecular.

Sodium nitride is an ionic compound. Draw a diagram that shows the formula of the compound, the charges on the ions and the arrangement of the valency electrons around the negative ion.

Use x to represent an electron from a sodium atom.
Use o to represent an electron from a nitrogen atom.

Separate: Chemistry and Extended Only

Silicon(IV) oxide has a macromolecular structure.

Carbon and silicon are elements in Group IV. Both elements have macromolecular structures.

Diamond and graphite are two forms of the element carbon.

Separate: Chemistry and Extended Only

Two of the oxides of these elements are carbon dioxide, CO₂, and silicon(IV) oxide, SiO₂.

The first three elements in Group IV are

   Carbon

   Silicon

   Germanium

The element germanium has a diamond-type structure. Describe the structure of germanium. A diagram is acceptable.

Unlike diamond, graphite is soft and is a good conductor of electricity.

Separate: Chemistry and Extended Only

Carbon dioxide and silicon(IV) oxide have similar formulae but different types of structure.

Extended Only 

Lead is an excellent roofing material. It is malleable and resistant to corrosion. Lead rapidly becomes coated with basic lead carbonate which protects it from further corrosion.

Lead has a typical metallic structure which is a lattice of lead ions surrounded by a ‘sea’ of mobile electrons. This structure is held together by attractive forces called a metallic bond.

[2]

[2]

Basic lead(II) carbonate is heated in the apparatus shown below. Water and carbon dioxide are produced.

Silica gel absorbs water. Silica gel often contains anhydrous cobalt(II) chloride. When this absorbs water it changes from blue to pink.
Suggest a reason.

Separate: Chemistry and Extended Only

Basic lead(II) carbonate has a formula of the type xPbCO₃.yPb(OH)₂ where x and y are whole numbers.
Determine x and y from the following information.

PbCO₃  → PbO + CO₂
Pb(OH)₂ → PbO + H₂O

When heated, the basic lead(II) carbonate gave 2.112 g of carbon dioxide and 0.432 g of water.

Mass of one mole of CO₂ = 44 g
Mass of one mole of H₂O = 18 g

Number of moles of CO₂ formed = .....................

[1]

Number of moles of H₂O formed = .....................

[1]

x = ..................... and y = .....................

Formula of basic lead(II) carbonate is ........................................................................

[1]

Extended Only

An ore of the important metal zinc is zinc blende, ZnS. This is changed into zinc oxide which is reduced to the impure metal by carbon reduction.

In common with most metals, zinc is a good conductor of electricity. It is used as an electrode in cells.

Extended Only

The following table gives information about six substances.

Which substance could be a metal?

State all the substances that are liquid at room temperature.

Separate: Chemistry and Extended Only 

Which substance could have a macromolecular structure similar to that of silicon(IV) oxide?

Which substance could be propane?

Which substance could be sodium chloride?

Separate: Chemistry and Extended Only 

Carbon dioxide and silicon(IV) oxide are oxides of Group IV elements.

Complete the following table.

Separate: Chemistry and Extended Only 

Separate: Chemistry Only 

Separate: Chemistry and Extended Only 

The table below shows the elements in the third period of the Periodic Table, the number of electrons in their outer energy  level, their oxidation state in their common compounds and their melting points.

Describe and explain the variation in oxidation state across the period.

Extended Only

The first three elements, Na, Mg and Al, are metals.

Describe the structure of a typical metal.

Extended Only

Explain why Na, Mg and Al are good conductors of electricity.

Which element exists as diatomic molecules of the type X₂?

Separate: Chemistry and Extended Only 

Silicon has a similar structure to diamond.

Explain why silicon has the highest melting point in the period.

Extended Only

Sodium chloride is a crystalline solid with a high melting point. It dissolves in water to give a neutral solution. Phosphorus trichloride is a liquid at room temperature. It reacts with water to form an acidic solution.

Suggest an explanation for these differences in properties.

Describe how you could show that magnesium oxide is a basic oxide and not an amphoteric oxide.

Extended Only

Draw a dot-and-cross diagram showing the bonding in magnesium oxide. Show outer electrons only.

The table shows the melting points, boiling points and electrical properties of five substances, A to E.

Choose a substance from the table above to match each of the following descriptions. A substance may be used once,  more than once or not at all. Justify each choice with evidence from the table.

One has been completed as an example.

This substance has a giant covalent structure:
Evidence:

Extended Only

This substance is a metal:
Evidence:

This substance is a liquid at room temperature.

This substance is an ionic solid. 

Separate: Chemistry and Extended Only 

Carbon and silicon are elements in Group IV. They both form oxides of the type XO₂

Silicon(IV) oxide, SiO₂, has a macromolecular structure.

 [3]

 [2]

Explain why the physical properties of carbon dioxide are different from those of diamond and silicon(IV) oxide.

Germanium is an element in Group IV. The electron distribution of a germanium atom is 2 + 8 + 18 + 4. It has oxidation states of +2 and +4.

Germanium forms a series of saturated hydrides similar to the alkanes.

[1]

[1]

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound germanium(IV) chloride, GeCl₄.

Use o to represent an electron from a chlorine atom.
Use x to represent an electron from a germanium atom.

Separate: Chemistry and Extended Only 

Describe the structure of the giant covalent compound germanium(IV) oxide, GeO₂.
It has a similar structure to that of silicon(IV) oxide.

Separate: Chemistry and Extended Only 

Is the change GeCl₂ to GeCl₄ reduction, oxidation or neither? Give a reason for your choice.

The first three elements in Group IV are carbon, silicon and germanium.
The elements and their compounds have similar properties.

The compound, silicon carbide, has a macromolecular structure similar to that of diamond. 

[3]

[2]

Separate: Chemistry and Extended Only 

Germanium(IV) oxide, GeO₂, has the same macromolecular structure as silicon(IV) oxide. Draw the structural formula of germanium(IV) oxide.

Germanium forms a series of hydrides comparable to the alkanes.

[1]

[2]

The properties of five alkenes at room temperature are shown in Table 1.1

Table 1.1

Answer this question using only the information in the table.

Suggest why the densities of the first three alkenes are much lower than the density of pentene and hexene.

The diagrams show part of the structures of five substances, A, B, C, D and E.

Answer the following question about these structures.

Which one of these structures, A, B, C, D or E, is used in cutting tools? 

Part of the structure of graphite is shown.

Use the information from the diagram to explain why graphite is used as a lubricant.

Separate: Chemistry and Extended Only 

The names of eight substances are given.

 aluminium oxide           calcium oxide       ethanol            nitrogen

                     iron(III) oxide          methane         oxygen         silicon(IV) oxide                   

State which substance is a macromolecular solid.

Carbon is an element which exists in different forms.

Name two forms of the element carbon that have giant covalent structures.

Extended Only 

Magnesium is a metal.

Describe the structure and bonding of metals. Include a labelled diagram in your answer.