1-5 Bonding In Compounds (part 4)

V. Bonding in compounds

Part 4

Topic

V.

Bonding in compounds

Reference Reading

Integrated Chemistry Today (2nd Ed.), L.H.M Chung, Book 1A, pg 93–94

Objectives

1.5.1.5 – recognise that some covalent substances exist as giant lattices as exemplified by diamond and quartz

Notes

6.

Page 1

Part 4

Giant covalent structure

Not all covalent substances possess molecular structure. Besides molecular compound, some covalent compound has a very large structure. In a small crystal of diamond, there is over 1,000,000,000,000,000,000 carbon atoms. The structure is called giant covalent lattice / structure. Diamond (A form of carbon) The carbon atoms are joined together tetrahedrally, each carbon atom is joined to other four carbon atoms by covalent bond. Since C–C is really strong, diamond has a really high melting point (3550ºC) because those strong C–C bond have to be broken upon melting.

Other examples : The structure of silicon is identical to that of diamond. However, the Si–Si bond is weaker, thus it has a lower melting point (1412ºC)

Quartz / Sand / silicon(IV) oxide / silicon oxide / silicon dioxide (SiO2) The structure of quartz is similar to that of diamond. Each silicon atom is joined to 4 oxygen atoms and each oxygen atom is then connected to another silicon atom. The silicon and oxygen are joined together by strong covalent bond. Upon melting, a lot of energy is required to break the Si–O covalent bond. Therefore, silicon(IV) oxide has a relatively high melting point 1610ºC.

giant covalent lattice / structure quartz (silicon(IV) oxide)

Glossary

diamond

Past Paper Questions 95 3 A

3

Which of the following correctly describes the structure of quartz ? A. giant covalent structure B. giant ionic structure C. giant metallic structure D. simple molecular structure