Chemistry, Third edition

REVISION QUESTIONS 81

Revision questions

5.1.Draw Lewis structures for the following:

(i)ICl 3 (ii)BeF 2 (iii)BFCl 2 (iv)XeF 2 (v)CH 2 Cl 2.

5.2.Determine the shapes of the molecules in Question 5.1.

5.3.Draw a Lewis structure for covalent HCN. Determine

the shape of the molecule.

5.4.Which of the following molecules have a dipole moment?

(i) SF 6 (ii)XeF 2 (iii)SO 3 (iv)SO 2 (v)CH 2 Cl 2.

5.5.What physical evidence is there for the existence of
London dispersion forces?

5.6.Which metal would you expect to have the highest

melting point K or Ca? Explain your reasoning.

5.7.Explain why diamond does not conduct electricity, but

graphite does.

5.8.Explain the type of intermolecular bonding that exists in

solid carbon dioxide (dry ice).

5.9.Water molecules have stronger hydrogen bonding

between them than ammonia molecules. Why?

5.10.Propanone (old name acetone) has the structure

Is it possible for molecules of propanone to hydrogen bond

together in the liquid state? Explain your reasoning

5.11.Since the discovery of buckminsterfullerene, a number

of carbon molecules with a similar spherical structure (called

fullerenes) have been made. It was once believed that any

fullerene smaller than C 60 would be too unstable to isolate in

bulk, but in 1998 the Zettl Research Group announced the

preparation of C 36. As with other fullerenes, the spherical

molecule of C 36 is composed of pentagons and hexagons of

carbon atoms. Using a model kit (or plasticine and straws)

can you make a model of the molecule and decide how many

hexagons and pentagons it contains?

Box 5.7

Relative strengths of London forces and hydrogen bonds

Are hydrogen bonds stronger than London

forces?Not necessarily, despite the fact that

the figures in Table 5.3 suggest this. The

dispersion forces between many very large

molecules, because they contain a large

number of electrons, cause those large

molecules to have a greater intermolecular

attraction than that between small molecules

such as water, even though hydrogen bonds

are present between water molecules.

Cooking oil contains molecules with high

molecular masses and therefore many

electrons. The London forces between the

molecules are so large that the oil has a

higher boiling point than water. Battered fish

and chips get their distinctive taste because

vaporized water makes holes in the batter and

potatoes. If oil did not have a much higher

boiling point than water, then battered fish and

chips would not have such a crispy texture.

Extension material to support this unit is available on our website. For more advanced theories of

bonding see Appendix 4 on the website.