Chem Bonding Section a Ans

Nanyang Junior College

H2/H1 Chemistry

JC1 2014

Chemical Bonding Tutorial Section A: Review Questions �� . �� , �� 3 �� . �� (�� ) �� , �� . �� 1.5 �� .

1

Which of the following statements explains why copper conducts electricity when a potential difference is applied? A B C D

2

3

Copper(II) ions move to the cathode The crystal lattice breaks down Electrons combine with copper(II) ions Bonding electrons in the crystal lattice move

Which bonding type does not correspond to its description of physical properties?

A

Bonding type Giant covalent

B C

Simple covalent Metallic

D

Ionic

Physical properties High melting point, conducts electricity when in solution but not when solid Low melting point, does not conduct electricity in any state Variety of melting points, conducts electricity when solid and when molten High melting point, conducts electricity when molten but not when solid

The C2H2 molecule is linear. What can be deduced from this about the numbers of molecule?

and

σ

bonds present in the

π

3

��

A B C D

σ

π

2 2 3 3

2 3 1 2

�2�2� ��

Page 1 of 18


4

H2/H1 Chemistry

JC1 2014

Why is the molecule of BCl3 planar, whereas the molecule of PH 3 is pyramidal? A The boron atom has no d-orbitals available for bonding. B The boron atom in BCl3 has 6 electrons in its valence shell, while the phosphorous atom in PH3 has 8. C The repulsion between chlorine atoms is greater than that between hydrogen atoms. D The covalent radius of phosphorus is greater than that of boron.

5

MBTE is a constituent of petrol.

3

�� ! �� 2��

What are the values of angle P and angle Q in a molecule of MTBE?

A B C D

6

Angle Q 105 180 105 180

AlCl3 reacts with LiAlH4 and (CH3)3N to give (CH3)3NAlH3. Which statement about (CH3)3NAlH3 is correct? A B C D

7

Angle P 90 90 109 109

It contains hydrogen bonding It is dimeric The Al atom is electron deficient The shape about the Al atom is tetrahedral

3

��

��

��

��

��

Why is the boiling point of methane greater than that of neon? [Ar: H, 1; C, 12; Ne, 20] A B C D

A molecule of methane has a greater mass than a molecule of neon. A molecule of methane has more electrons than a molecule of neon. Molecules of methane have stronger intermolecular forces than those of neon. Molecules of methane form hydrogen bonds, but those of neon do not.

Page 2 of 18

2


8

JC1 2014

Which of the following solids consists of atoms or molecules held together only by van der Waals’ forces? A B C D

9

H2/H1 Chemistry

CO2 Cu H2O MgO

Which of the following molecules will not form a hydrogen bond with another of its own molecules? 3

��

A B C D

CH3CHO CH3NH2 CH3OH NH3

��

��

��

��

��

10 When heated, solid iodine readily forms iodine vapour. What does this information suggest about the nature of the particles in these 2 physical states of iodine?

A B C D

Solid ionic ionic molecular molecular

Vapour atomic molecular atomic molecular

11 Which set of properties could apply to a non-ionic compound which has a giant lattice?

A B C D

Physical state temperature liquid liquid solid solid

at

room

Electrical conductivity molten state Does not conduct Does not conduct Conducts well Does not conduct

Page 3 of 18

in

Melting point / C -114 Melts over a range 808 1610


H2/H1 Chemistry

JC1 2014

The responses A to D should be selected on the basis of A 1, 2 and 3 are correct

B 1 and 2 only are correct

C 2 and 3 only are correct

D 1 only is correct

No other combination of statements is used as a correct response.

12 Which of the following are features of the structure in metallic copper? 1 2 3

Ionic bonds Delocalised electrons Lattice of ions

13 In microwave ovens, the wave energy produced is absorbed by certain polar molecules. Which of the following would absorb microwave energy? 1 2 3

C2H5OH NaCl SiO2

14 The boiling points of pentane and 2,2-dimethylpropane are 36 C and 9 C respectively. Which of the following suggested factors help to account for this difference in boiling points?

Pentane 1 2 3

2,2-dimethylpropane

The molecule of 2,2-dimethylpropane is more compact than that of pentane. The covalent bonds in pentane are stronger than those in 2,2-dimethylpropane. There is more effective hydrogen bonding in pentane than in 2,2-dimethylpropane.

15 Many ceramic materials based on silicon(IV) oxide have recently been developed. Which properties apply to these materials? 1 2 3

They are heated during manufacture and form solids. They are heat-resistant solids. They are good conductors of electricity due to delocalised electrons.

Page 4 of 18


H2/H1 Chemistry

JC1 2014

16 a) Explain what is meant by sigma (σ) and pi ( π) bonds. Illustrate your answers with suitable diagrams. Refer to lecture notes Page 13 and 14.

b) How many sigma (σ) and pi (π) bonds are present in the propene (C 3H6) molecule? 3

��

8σ, 1π

��

��

��

��.

��

�� .

17 For the following particles, • draw their dot-and-cross diagrams • count the total number of lone pairs and bond pairs • state their shapes according to VSEPR theory • draw their shapes • give the bond angles about the central atom state whether they are polar or non polar (only applicable for molecules) • Bond pairs / Lone pairs

Shape, Bond Angle, Polarity

NF3

3 bp 1 lp

Trigonal pyramidal 107 º Polar

SiF4

4 bp 0 lp

tetrahedral 109 º Non Polar

Particle

Dot-and-cross diagram / Structure

Page 5 of 18

��


H2/H1 Chemistry

JC1 2014 Bond pairs / Lone pairs


CH2Cl2

4 bp 0 lp

tetrahedral 109 º Polar

ICl3

3 bp 2lp

T shape 90 º Polar

Particle


3

�� , ��

ClO

��

2 bp 2 lp

NH2

H3O+

3 bp 1 lp

NO3 

3 bp 0 lp

Page 6 of 18

Bent 105 º

Trigonal pyramidal 107 º

Trigonal planar 120 º


H2/H1 Chemistry

JC1 2014 Bond pairs / Lone pairs


AlH4 

4 bp 0 lp

tetrahedral 109 º

BrCl2 

2 bp 3 lp

Linear 180 º

I3 

2 bp 3 lp

Linear 180 º

SO42 

4 bp 0 lp

tetrahedral 109 º

Particle


18 a) Describe the bonding present in

3

��

��

��

��

(i) solid krypton,

36Kr,

Solid krypton exists as a lattice of atoms with weak van der Waals forces between Kr atoms. (ii) solid rubidium,

37Rb.

Rubidium has a giant metallic lattice with strong metallic bonds between the cations and the sea of delocalised electrons.

Page 7 of 18


H2/H1 Chemistry

JC1 2014

b) Use your descriptions of their bonding to explain why the boiling point of krypton is −152°C whereas that of rubidium is 686°C, despite their having nearly the same relative atomic mass, Ar. 3

��

More energy is required to overcome the stronger metallic bonds in Rb than the weak van der Waals forces in Kr. Hence Rb has a higher b.p. than Kr.

�� . �� ) �� . ��

19 The table below gives the boiling points of four organic compounds:

A B C D

formula CH3CH2CH2CH2CH3 (CH3)4C CH3CH2CH2CH2OH CH3CH2OCH2CH3

relative molecular mass 72 72 74 74

boiling point / oC 36 10 117 35

By comparing i) A with B, ii) A with C and iii) C with D, suggest explanations for the differences in the boiling points within each of the three pairs. i)

3

��

A with B

��,

��,

��

Both A and B have simple molecular structure with weak van der Waals’ forces between molecules.

�� /�� !

A has a straight chain structure while B has a more spherical shape due to its highly branched structure. The vdW forces between A molecules are stronger than that of B due to the large surface area of contact. More energy is required to overcome the stronger vdW forces, higher bp.

ii) A with C Both A and C have simple molecular structure. There are weak van der Waals’ forces between A molecules, and H-bonds between C molecules. More energy is required to overcome the stronger H-bonds than vdW forces, so C has a higher bp.

iii) C with D Both C and D have simple molecular structure. There are H-bonds between C molecules and pd-pd interactions between D molecules. More energy is required to overcome the stronger H-bonds than pd-pd interactions, so C has a higher bp.

Page 8 of 18


H2/H1 Chemistry

JC1 2014

20 Explain the following observations in terms of the structure and bonding present. a) 4-hydroxybenzoic acid is more soluble in water than 2-hydroxybenzoic acid. O

OH O

OH OH

OH

4-hydroxybenzoic acid

2-hydroxybenzoic acid 3

•

• •

•

In 2-hydroxybenzoic acid, –COOH and –OH groups are close to each other. They can form intramolecular H-bonds This reduces the chance of forming H-bonds with water molecules. Hence it is less soluble in water

�� 37 �� . ��, �� , �� . ��

b) In benzene solution, the measured relative molecular mass of methanoic acid is approximately 92.0. Explain the observation and include a relevant diagram in your answer. 3

In benzene solution, methanoic acid dimerises through hydrogen bonds.

��

Page 9 of 18

Chem Bonding Section a Ans

Recommend Documents