IGCSE Chemistry

Year 10. Topic 4. Structure and bonding Updated 31 March 2003

5 weeks

Topic / Syllabus statements / Study tasks / activities / Practical work / Resources / Book References
Models in chemistry / Start off with some familiar models, like maps – three different ones are printed on p.89. Discuss the limitations and uses of these maps. Can the class think of any other models, limitations and advantages? (Discuss qu.5 p.89 on the limitations of maps and models)
Write the names of some common substances on the board and show the class how to make models of their molecules using a model kit. Then use model kits to make models of the molecules in fig.5.15 p.89, and then do qu.6 p.89.
Hand out data books and use sections 2-3 to do qu.7&8 p.91
Summarise by emphasizing that no model is adequate to describe the true nature of reality: diagrams and 3D models are always to be taken ‘with a pinch of salt.’
Teacher’s notes
The page numbers in the SoW refer to the Nuffield science: Chemistry students book.
Covalent bonding / Describe the formation of single covalent bonds

Describe the electron arrangement in more complex covalent molecules such as N2, C2H4, CH3OH and CO2

/ Introduce the two main bonding types and ask students to come up with a list of common substances, which you can then classify as covalent or ionic for them. Given the two sets of compounds, ask the class what is similar and what is different about the groups.
Use hydrogen as the first example – draw the bonding diagram and make sure the students understand that the bond is the electron pair. Go on to draw fluorine, water and ammonia. Go on to double bonds in oxygen and carbon dioxide, and triple bonds in nitrogen.
Discuss the reason for the low boiling points of simple molecular compounds and emphasise that the covalent bond is very strong and cannot be disrupted by heat.
Do qu.9-10 pp.91-2.
Homework:
Ask students to find out why water has an unusually high boiling point. / Ramsden pp.75-77
Giant covalent structures / Describe giant covalent structures (diamond and graphite)
Relate these structures to uses
Describe the macromolecular structure of silicon (IV) oxide
Describe the similarity in properties between diamond and SiO2, related to their structures / Review the properties of molecular compounds and then introduce diamond and graphite as covalently bonded compounds. Emphasise the difference in properties and then show the class a diagram of diamond. The reason for the differences in properties should now be clear.
Do qu.11-13 p.96
Homework:
Ask students to draw the structure of aluminium oxide / Demo the conductivity of pencil lead and discuss the reasons for the difference in conductivity between graphite and diamond. Students can then draw diagrams of diamond, graphite and silicon dioxide.
Ionic bonding / Describe the formation of ionic bonds between elements from Groups I and VII
Describe the formation of ionic bonds between metallic and non-metallic elements
Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions

Understand valence

/ Go back to the lists of ionic and covalent compounds produced in lesson 3 and review the properties of ionic compounds. Alternatively, students can test some ionic salts for:
·  solubility water and acetone
·  conductivity of the solid and the solution
·  melting point
Discuss the structure of NaCl using a model and the diagram on p.97 and elicit from this reasons for the properties of ionic compounds. In particular, discuss the need for charge carriers which are free to move as the two requirements for conduction.
Students should draw a diagram of NaCl and then do qu.14-16 p.97 and qu.17-19 p.99
Homework:
Ramsden p.82 q.22, 23. (Revision of the differences between all kinds of bonding)
/ Demo practicals to show evidence for the existence of ions (copper chromate gel in U – tube, etc.)
Formulae of compounds / / Get students to work out the formulae (by drawing bonding diagrams) for some tricky compounds, such as aluminium oxide, beryllium nitride, carbon disulphide, etc.. and then introduce the idea that there is an easier way of working out formulae. Introduce valency as the number of electrons to be gained or lost in the outer shell, and show the class how to work out formulae.
Then do Qu.20-22 p.100 and Qu.1-3 Ramsden p.75 / Box 213 (working out ionic formulae)
Metals
Alloys / Describe alloys, such as brass, as a mixture of metals
Describe metallic bonding as a lattice of positive ions in a sea of electrons and use this to describe the electrical conductivity and malleability of metals
Rules for predicting structure / Discuss the structure, properties and uses of metals. In particular, note the difference in conduction mechanism between ionic solutions and metals. Grains and imperfections in structure can be demonstrated with small beads on the OHP.
A list of alloys and their uses can be found in Ramsden p.218 and alloys / Metallic bonding: Ramsden p.210-211
Alloys: Ramsden p.218
Rules for determining structure / / In this lesson, students are trying to come up with a set of rules based on physical properties for determining the type of structure of a compound. The rules can either be in the form of a dichotomous key, a flow chart, or simply a list of requirements for each structural class. Emphasise the importance of following the instructions carefully, not heating too strongly, for example. / Lab activity C5A – working out rules for predicting structure (see p.249 in teachers’ guide)
Alternative sheet: How does the type of chemical bond affect the properties of a chemical substance?
Rules for determining structure / / Qu.23-26 p.101. / Use the key on p.101 to experimentally determine the structure of some substances. / Help sheet: Which substances conduct electricity?
Structure – property relationship / Describe the differences in volatility, solubility and electrical conductivity between ionic and covalent compounds
Making glass
/ Make a table summarizing the differences between ionic and covalent compounds (eg. Ramsden p.79)
Revision questions (Ramsden qu.1-4 p.80 & 1-24 pp.81-3)
Sheet C5D (Bragg and crystallography) / Summary of properties: Ramsden p.79
Making glass (sheet)

Note: Page numbers refer to Nuffield chemistry unless otherwise indicated