Training Presentation

1
The Halogens
41.1 Characteristic Properties of the
Halogens 41.2 Variation in Properties of the
Halogens 41.3 Comparative Study of the Reactions
of Halide Ions 41.4 Acidic Properties of
Hydrogen Halides and the Anomalous Behaviour of
Hydrogen Fluoride
2
Characteristic Properties of the Halogens
3
41.1 Characteristic Properties of the Halogens
(SB p.78)
Introduction

• Group VIIA elements include
• ? fluorine
• ? chlorine
• ? bromine
• ? iodine
• ? astatine

4
41.1 Characteristic Properties of the Halogens
(SB p.78)
Introduction

• Astatine
• ? not much is known
• ? radioactive

5
41.1 Characteristic Properties of the Halogens
(SB p.78)
Introduction

• Group VIIA elements
• ? also called halogens

6
41.1 Characteristic Properties of the Halogens
(SB p.78)
The halogens
7
41.1 Characteristic Properties of the Halogens
(SB p.79)
Introduction

• All halogens
• ? outermost shell electronic configuration
  of ns2np5
• ? one electron short of the octet electronic
  configuration

8
41.1 Characteristic Properties of the Halogens
(SB p.79)
Introduction

• In the free elemental state
• ? form diatomic molecules
• ? complete their octets by sharing their
  single unpaired p electrons

9
41.1 Characteristic Properties of the Halogens
(SB p.79)
Introduction

• When halogens react with other elements
• ? complete their octets
• ? depending on the electronegativity of the
  element

10
41.1 Characteristic Properties of the Halogens
(SB p.79)
Introduction

• Either
• ? gaining an additional electron to form
  halide ions
• ? or sharing their single unpaired p
  electrons to form single covalent bonds

11
41.1 Characteristic Properties of the Halogens
(SB p.79)
chlorine
Appearances of halogens at room temperature and
pressure chlorine
12
41.1 Characteristic Properties of the Halogens
(SB p.79)
bromine
Appearances of halogens at room temperature and
pressure bromine
13
41.1 Characteristic Properties of the Halogens
(SB p.79)
iodine
Appearances of halogens at room temperature and
pressure iodine
14
41.1 Characteristic Properties of the Halogens
(SB p.79)
High Electronegativity
Electronegativity is the relative tendency of an
atom to attract bonding electrons towards itself
in a covalent bond.
15
41.1 Characteristic Properties of the Halogens
(SB p.79)
High Electronegativity

• All halogens
• ? high electronegativity values
• ? high tendency to attract an additional
  electron to achieve the stable octet
  electronic configuration
• ? highest among the elements in the same
  period

16
41.1 Characteristic Properties of the Halogens
(SB p.79)
Electronegativity values of halogens
17
41.1 Characteristic Properties of the Halogens
(SB p.79)
High Electron Affinity
Electron affinity is the enthalpy change when one
mole of electrons is added to one mole of atoms
or ions in the gaseous state.
18
41.1 Characteristic Properties of the Halogens
(SB p.79)
High Electron Affinity

• Its value
• ? indicates the ease of formation of anions

19
41.1 Characteristic Properties of the Halogens
(SB p.79)
High Electron Affinity

• All halogens
• ? negative values of electron affinity
• ? high tendency to attract an additional
  electron to form the respective halide ions

20
41.1 Characteristic Properties of the Halogens
(SB p.79)
Electron affinities of halogens
21
41.1 Characteristic Properties of the Halogens
(SB p.80)
Bonding and Oxidation State

• Halogens
• ? gain an additional electron to form the
  halide ions
• ? combine with metals to form metal halides
• ? held together by ionic bonding

22
41.1 Characteristic Properties of the Halogens
(SB p.80)
Bonding and Oxidation State

• The oxidation states of the halogens 1

23
41.1 Characteristic Properties of the Halogens
(SB p.80)
Bonding and Oxidation State

• The halogen atoms
• ? share their unpaired p electrons with a
  non-metallic atom
• ? form a covalent bond

24
41.1 Characteristic Properties of the Halogens
(SB p.80)
Bonding and Oxidation State

• Halogens (except fluorine)
• ? exhibit an oxidation state of 1 or 1 in
  the covalent molecules formed
• ? depend on the electronegativity of the
  elements that are covalently bonded with the
  halogens

25
41.1 Characteristic Properties of the Halogens
(SB p.80)
Bonding and Oxidation State

• All halogens (except fluorine)
• ? can expand their octets of electrons by
  utilizing the vacant, low-lying d orbitals

26
41.1 Characteristic Properties of the Halogens
(SB p.80)
Bonding and Oxidation State

• Each of these halogen atoms
• ? have variable numbers of unpaired electrons
  to pair up with electrons from other atoms
• ? able to form compounds of different
  oxidation states

27
41.1 Characteristic Properties of the Halogens
(SB p.80)
Electrons-in-boxes diagrams of the electronic
configuration of a halogen atom of the ground
state and various excited states
28
41.1 Characteristic Properties of the Halogens
(SB p.81)
Various oxidation states of halogens in their
ions or compounds
29
41.1 Characteristic Properties of the Halogens
(SB p.81)
Various oxidation states of halogens in their
ions or compounds
30
41.1 Characteristic Properties of the Halogens
(SB p.81)
Bonding and Oxidation State

• Fluorine
• ? cannot expand its octet
• ? no low-lying empty d orbitals available
• ? the energy required to promote electrons
  into the third quantum shell is very high

31
41.1 Characteristic Properties of the Halogens
(SB p.81)
Bonding and Oxidation State

• Fluorine
• ? the most electronegative element
• ? only one unpaired p electron available for
  bonding
• ? oxidation state is limited to 1

32
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• All halogens
• ? coloured
• ? the absorption of radiation in the visible
  light region of the electromagnetic spectrum

33
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• The absorbed radiation
• ? the excitation of electrons to higher
  energy levels

34
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• Fluorine atom
• ? smaller size
• ? absorb the radiation of relatively high
  frequency (i.e. blue light)
• ? appears yellow

35
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• Atoms of other halogens
• ? larger sizes
• ? absorb radiation of lower frequency

36
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• Iodine
• ? absorbs the radiation of relatively low
  frequency (i.e. yellow light)
• ? appears violet

37
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• Halogens
• ? different colours when dissolved in
  different solvents

38
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colour

• Halogens
• ? non-polar molecules
• ? not very soluble in polar solvents (such as
  water)
• ? but very soluble in organic solvents (such
  as 1,1,1-trichloroethane)

39
41.1 Characteristic Properties of the Halogens
(SB p.82)
Colours of halogens in pure form and in solutions
40
41.1 Characteristic Properties of the Halogens
(SB p.82)
(a)
(b)
(c)
Colours of halogens in water(a) chlorine (b)
bromine (c) iodine
41
41.1 Characteristic Properties of the Halogens
(SB p.83)
(a)
(b)
(c)
Colours of halogens in 1,1,1-trichloroethane(a)
chlorine (b) bromine (c) iodine
42
41.1 Characteristic Properties of the Halogens
(SB p.83)
43
41.2 Variation in Properties of the Halogens (SB
p.83)
Introduction

• All halogens
• ? exist as diatomic molecules

44
41.2 Variation in Properties of the Halogens (SB
p.83)
Introduction

• In the diatomic molecules
• ? the halogen atoms are held together by
  strong covalent bonds

45
41.2 Variation in Properties of the Halogens (SB
p.83)
Introduction

• The molecules
• ? only held together by weak van der Waals
  forces (i.e. instantaneous dipole-induced
  dipole interaction)

46
41.2 Variation in Properties of the Halogens (SB
p.83)
Introduction

• The physical properties of halogens
• ? strongly affected by the way that the atoms
  are joined together
• ? the interactions that hold the molecules
  together

47
41.2 Variation in Properties of the Halogens (SB
p.83)
Some physical properties of the halogens
48
41.2 Variation in Properties of the Halogens (SB
p.83)
Some physical properties of the halogens
49
41.2 Variation in Properties of the Halogens (SB
p.84)
Variation in Physical Properties
1. Melting Point and Boiling Point

• Halogens
• ? exist as non-polar diatomic molecules

50
41.2 Variation in Properties of the Halogens (SB
p.84)
1. Melting Point and Boiling Point

• Going down the group
• ? the melting points and boiling points of
  halogens increase

51
41.2 Variation in Properties of the Halogens (SB
p.84)
1. Melting Point and Boiling Point

• These physical properties depend on
• ? the strength of van der Waals forces
  holding the halogen molecules together

52
41.2 Variation in Properties of the Halogens (SB
p.84)
1. Melting Point and Boiling Point

• Going down the group
• ? the molecular size increases
• ? the electron clouds of the molecules become
  larger
• ? more polarizable

53
41.2 Variation in Properties of the Halogens (SB
p.84)
1. Melting Point and Boiling Point

• Instantaneous dipoles
• ? more readily formed
• ? the instantaneous dipole-induced dipole
  interaction between the molecules is stronger

54
41.2 Variation in Properties of the Halogens (SB
p.84)
1. Melting Point and Boiling Point

• A greater amount of energy is required
• ? separate the molecules in the processes of
  melting and boiling
• ? the melting points and boiling points
  increase progressively from fluorine to
  astatine

55
41.2 Variation in Properties of the Halogens (SB
p.84)
Variations in melting point and boiling point of
the halogens
56
41.2 Variation in Properties of the Halogens (SB
p.84)
2. Electronegativity
Electronegativity is the relative tendency of the
nucleus of an atom to attract bonding electrons
towards itself in a covalent bond.
57
41.2 Variation in Properties of the Halogens (SB
p.84)
2. Electronegativity

• Going down the group
• ? the electronegativity values of halogens
  decrease

58
41.2 Variation in Properties of the Halogens (SB
p.84)
2. Electronegativity

• Going down the group
• ? the atomic size increases
• ? the number of electron shells increases
• ? creates a greater screening effect

59
41.2 Variation in Properties of the Halogens (SB
p.84)
2. Electronegativity

• The atomic size increases
• ? The tendency of the nucleus of the halogen
  atom attract bonding electrons towards itself
  in a covalent bond decreases

60
41.2 Variation in Properties of the Halogens (SB
p.85)
Variations in electronegativity value of the
halogens
61
41.2 Variation in Properties of the Halogens (SB
p.85)
3. Electron Affinity
Electron affinity of halogens is the enthalpy
change when one mole of electrons is added to one
mole of halogen atoms in the gaseous state.
62
41.2 Variation in Properties of the Halogens (SB
p.85)
3. Electron Affinity

• The electron affinity
• ? increases from fluorine to chlorine
• ? decreases from chlorine to astatine

63
41.2 Variation in Properties of the Halogens (SB
p.85)
3. Electron Affinity

• The general decrease in electron affinity
• ? the atomic size increases
• ? the number of electrons shells down the
  group increases
• ? the effective nuclear charge decreases
• ? tendency of the nuclei of halogen atoms to
  attract additional electrons decreases

64
41.2 Variation in Properties of the Halogens (SB
p.85)
3. Electron Affinity

• Fluorine
• ? abnormally low electron affinity

65
41.2 Variation in Properties of the Halogens (SB
p.85)
3. Electron Affinity

• Fluorine atom
• ? very small atomic size
• ? energy is required to overcome the
  repulsion between the additional electron
  and the electrons present in the electron shell

66
41.2 Variation in Properties of the Halogens (SB
p.85)
Variations in electron affinity of the halogens
67
41.2 Variation in Properties of the Halogens (SB
p.86)
68
41.2 Variation in Properties of the Halogens (SB
p.86)
Variation in Chemical Properties

• Halogens
• ? the most reactive group of non- metallic
  elements
• ? all halogens have one electron short of the
  octet electronic configuration
• ? tend to attract an additional electron to
  attain the octet electronic configuration

69
41.2 Variation in Properties of the Halogens (SB
p.86)
Variation in Chemical Properties

• Halogens
• ? highly electronegative
• ? highly negative electron affinity values
• ? strong oxidizing agents

70
41.2 Variation in Properties of the Halogens (SB
p.86)
Variation in Chemical Properties

• Fluorine
• ? very strong oxidizing agent

71
41.2 Variation in Properties of the Halogens (SB
p.86)
Variation in Chemical Properties

• Other elements that combine with fluorine
• ? have their highest possible oxidation numbers

72
41.2 Variation in Properties of the Halogens (SB
p.86)
1. Relative Oxidizing Power of Halogens
Reactions with Sodium

• All halogens
• ? combine directly with sodium to form sodium
  halides
• ? the reactivity decreases down the group
  from fluorine to iodine

73
41.2 Variation in Properties of the Halogens (SB
p.86)
Reactions with Sodium

• Fluorine
• ? react explosively to form sodium fluoride
• 2Na(s) F2(g) ?? 2NaF(s)

74
41.2 Variation in Properties of the Halogens (SB
p.86)
Reactions with Sodium

• Chlorine
• ? react violently to form sodium chloride
• 2Na(s) Cl2(g) ?? 2NaCl(s)

75
41.2 Variation in Properties of the Halogens (SB
p.86)
Reactions with Sodium

• Bromine
• ? burns steadily in bromine vapours to form
  sodium bromide
• 2Na(s) Br2(g) ?? 2NaBr(s)

76
41.2 Variation in Properties of the Halogens (SB
p.86)
Reactions with Sodium

• Iodine
• ? burns steadily in iodine vapours to form
  sodium iodide
• 2Na(s) I2(g) ?? 2NaI(s)

77
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions

• Aqueous chlorine
• ? oxidizes green iron(II) ions to yellowish
  brown iron(III) ions

78
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions

• Aqueous bromine
• ? oxidizes green iron(II) ions to yellowish
  brown iron(III)

79
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions

• Iodine
• ? a mild oxidizing agent
• ? not strong enough to oxidize iron(II) ions.

80
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions

• The spontaneity of a reaction can be worked out
• ? adding the standard electrode potentials
  of the two half reactions concerned

81
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions
? the reaction is predicted to be spontaneous
82
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions

• Aqueous chlorine and bromine

? the oxidation reactions of aqueous iron(II)
ions are spontaneous
83
41.2 Variation in Properties of the Halogens (SB
p.87)
Standard electrode potentials of some related
half reactions
84
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Iron(II) Ions

• Aqueous iodine

? this reaction is not spontaneous
85
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Thiosulphate Ions

• Thiosulphate ions
• ? a reducing agent
• ? reacts differently with halogens of
  different oxidizing power

86
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Thiosulphate Ions

• Iodine
• ? reacts with sodium thiosulphate to form
  sodium tetrathionate and sodium iodide

87
41.2 Variation in Properties of the Halogens (SB
p.87)
Reactions with Thiosulphate Ions

• This is a typical reaction
• ? determine the concentration of iodine in a
  solution
• ? by titration with standard thiosulphate
  solution (iodometric titration)
• I2(aq) 2S2O32(aq) ?? 2I(aq)
  S4O62(aq)

88
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions with Thiosulphate Ions

• Chlorine and bromine
• ? more powerful oxidizing agents
• ? oxidize thiosulphate ions to sulphate(VI)
  ions

89
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions with Thiosulphate Ions

• Chlorine
• 4Cl2(aq) S2O32(aq) 5H2O(l) ?? 8Cl(aq)
  2SO42(aq) 10H(aq)

90
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions with Thiosulphate Ions

• Bromine
• 4Br2(aq) S2O32(aq) 5H2O(l) ??
  8Br(aq) 2SO42(aq) 10H(aq)

91
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions of halogens with sodium
92
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions of halogens with iron(II) ions
93
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions of halogens with thiosulphate ions
94
41.2 Variation in Properties of the Halogens (SB
p.88)
Reactions with Thiosulphate Ions

• The relative oxidizing power of the halogens
  decreases in the order
• F2 gt Cl2 gt Br2 gt I2

95
41.2 Variation in Properties of the Halogens (SB
p.89)
2. Disproportionation of the Halogens in Water
and Alkalis
Reactions with Water

• Fluorine
• ? reacts vigorously with water to form
  hydrogen fluoride and oxygen
• 2F2(g) 2H2O(l) ?? 4HF(aq) O2(g)

96
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Chlorine
• ? less reactive than fluorine
• ? reacts with water to form hydrochloric acid
  and chloric(I) acid (also known as
  hypochlorous acid

97
41.2 Variation in Properties of the Halogens (SB
p.89)
98
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• The oxidation number of chlorine
• ? decreases from 0 in Cl2(g) to 1 in HCl(aq)
• ? increases from 0 in Cl2(g) to 1 in HOCl(aq)

99
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Cl2(g)
• ? simultaneously oxidized and reduced
• ? an example of disproportionation

100
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water
Disproportionation is a chemical change in which
oxidation and reduction of the same species
(which may be a molecule, atom or ion) take place
at the same time.
101
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Chlorine water
• ? a mixture of hydrochloric acid and
  chloric(I) acid

102
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Chlorate(I) ion (also known as hypochlorite ion)
• ? an unstable ion
• ? decomposes when exposed to sunlight or high
  temperatures to give chloride ions and oxygen
• 2OCl(aq) ?? 2Cl(aq) O2(g)

103
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Chlorate(I) ion
• ? able to oxidize dyes to form colourless
  compounds
• ? bleaching power

104
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Chlorate(I) ion

OCl(aq) dye ?? Cl(aq) (dye O)
coloured colourless
105
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• Bromine
• ? only slightly soluble in water
• ? mainly exists as molecules in saturated
  bromine water

106
41.2 Variation in Properties of the Halogens (SB
p.89)
Reactions with Water

• When the solution is diluted
• ? hydrolysis takes place
• ? hydrobromic acid and bromic(I) acid (also
  called hydrobromous acid) are formed

107
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Water

• Bromate(I) ion
• ? also unstable
• ? forms colourless compounds when reacting
  with dyes
• OBr(aq) dye coloured ??
  Br(aq) (dye O)
  colourless

108
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Water

• Iodine
• ? does not react with water
• ? only slightly soluble in water

109
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Water

• Iodine
• ? soluble in potassium iodide solution
• ? exists as triiodide ions in the solution
• ? often called iodine solution
• I2(s) KI(aq) ?? KI3(aq) iodine
  solution

110
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• All halogens
• ? react with aqueous alkalis

111
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• The reactions between halogens and aqueous
  alkalis
• ? disproportionation (except fluorine)

112
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• Halogens
• ? react differently under cold / hot and
  dilute / concentrated conditions

113
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• In general
• ? their reactivities decrease down the group

114
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• Fluorine is passed through a cold and very dilute
  (2) sodium hydroxide solution
• ? oxygen difluoride (OF2) is formed
• 2F2(g) 2NaOH(aq) 0 cold, very
  dilute
• ?? 2NaF(aq) OF2(g) H2O(l) 1
  1

115
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• When fluorine is passed through a hot and
  concentrated sodium hydroxide solution
• ? oxygen is formed instead
• 2F2(g) 4NaOH(aq) 0
  2 hot, concentrated
• ?? 4NaF(aq) O2(g) 2H2O(l)
  1 0

116
41.2 Variation in Properties of the Halogens (SB
p.90)
117
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• Chlorine
• ? reacts with cold and dilute sodium
  hydroxide solution to form sodium chloride
  and sodium chlorate(I) (also called sodium
  hypochlorite)
• Cl2(aq) 2NaOH(aq) 0 cold,
  dilute ?? NaCl(aq) NaOCl(aq) H2O(l)
  1 1

118
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• Chlorine
• ? reacts with hot and concentrated sodium
  hydroxide solution to form sodium chloride and
  sodium chlorate(V)
• 3Cl2(aq) 6NaOH(aq) 0 hot,
  concentrated ?? 5NaCl(aq) NaClO3(aq)
  3H2O(l) 1 5

119
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• Bromine
• ? undergoes similar reactions with alkalis as
  chlorine
• ? sodium bromate(I) formed is unstable

120
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• Sodium bromate(I) formed
• ? disproportionates to form sodium bromide
  and sodium bromate(V) readily at room
  temperature and pressure
• ? reversible

121
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis
Br2(aq) 2NaOH(aq) cold, dilute ??
NaBr(aq) NaOBr(aq) H2O(l)
122
41.2 Variation in Properties of the Halogens (SB
p.90)
Reactions with Alkalis

• The chemical equation for the overall reaction
• 3Br2(aq) 6NaOH(aq) 0 cold,
  dilute?? 5NaBr(aq) NaBrO3(aq) 3H2O(l)
  1 5

123
41.2 Variation in Properties of the Halogens (SB
p.91)
Reactions with Alkalis

• Iodine
• ? behaves similarly as bromine

124
41.2 Variation in Properties of the Halogens (SB
p.91)
Reactions with Alkalis

• Except that the reaction with a cold and dilute
  alkali
• ? reversible

125
41.2 Variation in Properties of the Halogens (SB
p.91)
Reactions with Alkalis

• The backward reaction
• ? often used to prepare standard iodine
  solution for iodometric titrations

126
41.2 Variation in Properties of the Halogens (SB
p.91)
Reactions with Alkalis

• Dissolving a known quantity of potassium
  iodate(V) in excess potassium iodide solution and
  dilute sulphuric(VI) acid
• ? generated a known amount of iodine solution
• KIO3(aq) 5KI(aq) 6H(aq) ?? 3I2(aq)
  3H2O(l) 6K(aq)

127
41.2 Variation in Properties of the Halogens (SB
p.91)
Reactions with Alkalis

• The iodine generated
• ? used to oxidize reducing agents
• ? such as sulphate(IV) ions and ascorbic
  acid (vitamin C)

128
41.2 Variation in Properties of the Halogens (SB
p.91)
Reactions with Alkalis

• Excess iodine
• ? can be determined by back titration with
  sodium thiosulphate solution
• I2(aq) 2S2O32(aq) ?? 2I(aq)
  S4O62(aq)

129
41.2 Variation in Properties of the Halogens (SB
p.91)
130
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• All metal halides
• ? basically ionic compounds
• ? the ionic character of metal halides
  decreases on going down from fluorides to
  iodides

131
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• Lithium fluoride
• ? ionic

132
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• Lithium iodide
• ? considerable covalent character

133
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• Chlorides, bromides and iodides
• ? similar solubilities in water

134
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• Fluorides
• ? anomalous properties

135
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• Silver chloride, silver bromide and silver iodide
• ? insoluble in water

136
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.91)
Introduction

• Silver fluoride
• ? soluble in water

137
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• The reactions of halogens with halide ions follow
  the order of relative oxidizing power
• F2 gt Cl2 gt Br2 gt I2

138
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Fluorine
• ? displace all other halogens from the
  corresponding halide ions
• F2(g) 2Cl(aq) ?? 2F(aq) Cl2(aq)
• F2(g) 2Br(aq) ?? 2F(aq) Br2(aq)
• F2(g) 2I(aq) ?? 2F(aq) I2(aq)

139
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Chlorine
• ? displace bromine and iodine from bromide
  and iodide ions respectively
• Cl2(aq) 2Br(aq) ?? Br2(aq) 2Cl(aq)
• Cl2(aq) 2I(aq) ?? I2(aq) 2Cl(aq)

140
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
(a)
(b)
The mixture of chlorine water with (a) potassium
bromide solution (b) potassium iodide solution
141
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Bromine
• ? displace iodine from iodide ions only
• Br2(aq) 2I(aq) ?? I2(aq) 2Br(aq)

142
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Iodine
• ? cannot displace the other halogens from the
  corresponding halide ions

143
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• The feasibility of redox reactions at standard
  states in aqueous solutions
• ? predicted by using the values of standard
  electrode potentials

144
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Adding up the standard cell electrode potentials
  of the two corresponding half reactions

145
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens
? spontaneous
146
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Consider whether the following redox reaction
  will take place at standard states
• Br2(aq) 2I(aq) ?? I2(aq) 2Br(aq)

147
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Considered as the combination of the following
  two equilibria competing with one another

148
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens
? more positive standard electrode potential
149
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Bromine
• ? higher tendency to gain electrons (i.e.
  stronger oxidizing power)

150
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens

• Therefore

151
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.92)
Reactions of Halogens
? a positive value ? proceed spontaneously
152
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of halide ions with halogens
153
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of halide ions with halogens
154
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• The most convenient way to carry out displacement
  reactions
• ? mix aqueous solutions of the halogens with
  aqueous solutions of potassium iodide,
  potassium bromide and potassium chloride
• ? shake them well

155
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• Iodine
• ? almost insoluble in water
• ? dissolves readily in a solution containing
  iodide ions

156
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• The soluble triiodide ion, I3, is formed in this
  way

157
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• Observing the colour changes
• ? difficult to determine whether certain
  reactions have taken place or not by only

158
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• To determine whether the reaction mixture
  contains bromine or iodine
• ? add a small amount of 1,1,1- trichloroethane
  to the reaction mixture

159
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• Any bromine or iodine present
• ? dissolve more readily in the organic
  solvent than in water

160
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• If the reaction mixture contains bromine
• ? the bromine will dissolve in the bottom
  organic layer
• ? give a deep orange colour

161
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Reactions of Halogens

• If the reaction mixture contains iodine
• ? the iodine will dissolve in the bottom
  organic layer
• ? give a violet colour

162
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
(a)
(b)
(a) If the reaction mixture contains bromine, the
bottom organic layer will appear deep orange (b)
If the reaction mixture contains iodine, the
bottom organic layer will appear violet.
163
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
164
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• Aqueous solutions of chlorides, bromides and
  iodides
• ? give precipitates when reacting with silver
  nitrate(V) solution
• ? a characteristic test to show the presence
  of halide ions (except fluoride ions)

165
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions
Ag(aq) Cl(aq) ?? AgCl(s) white
precipitate Ag(aq) Br(aq) ??
AgBr(s) pale yellow precipitate Ag(aq)
I(aq) ?? AgI(s) yellow precipitate
166
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• All silver halides
• ? insoluble in acids

167
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• Dilute nitric(V) acid should be added before
  silver nitrate(V) solution
• ? remove interfering ions
• ? like sulphate (IV) ions or carbonate ions

168
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• The formation of the white precipitate ofsilver
  sulphate(IV) or silver carbonate
• ? may be mistaken as silver halides, can be
  prevented
• 2H(aq) SO32(aq) ?? SO2(g) H2O(l)
• 2H(aq) CO32(aq) ?? CO2(g) H2O(l)

169
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
AgCl(s)
Formation of silver halides silver chloride
170
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
AgBr(s)
Formation of silver halides silver bromide
171
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
AgI(s)
Formation of silver halides silver iodide
172
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• The formation of silver chloride, silver bromide
  and silver iodide
• ? identified by their colours
• ? or by their reactions with aqueous ammonia

173
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• Silver chloride
• ? dissolves readily in aqueous ammonia
• ? the formation of the complex
  diamminesilver(I) ion (Ag(NH3)2(aq))
• ? soluble in water

174
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions
AgCl(s) 2NH3(aq) ?? Ag(NH3)2(aq)
Cl(aq)
175
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• Silver bromide
• ? slightly soluble in aqueous ammonia

176
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.94)
Reactions with Silver Ions

• Silver iodide
• ? insoluble in aqueous ammonia

177
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with Silver Ions

• When exposed to sunlight
• ? silver chloride turns grey
• ? silver bromide turns yellowish grey
• ? silver iodide remains yellow

178
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with Silver Ions

• The colour changes of silver chloride andsilver
  bromide
• ? photochemical decomposition of the silver
  halides into their constituent elements (i.e.
  silver and halogens)

179
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Action of acidified silver nitrate(V) solution on
halides
180
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with ConcentratedSulphuric(VI) Acid

• Concentrated sulphuric(VI) acid
• ? an oxidizing acid
• ? exhibits both oxidizing and acidic
  properties

181
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with ConcentratedSulphuric(VI) Acid

• On treatment with concentrated sulphuric(VI) acid
• ? fluorides and chlorides give hydrogen
  fluoride and hydrogen chloride respectively

182
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with ConcentratedSulphuric(VI) Acid

• Example
• NaF(s) H2SO4(l) ?? NaHSO4(s) HF(g)
• NaCl(s) H2SO4(l) ?? NaHSO4(s) HCl(g)

183
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with ConcentratedSulphuric(VI) Acid

• Bromides and iodides
• ? do not give hydrogen bromide and hydrogen
  iodide respectively
• ? sulphur dioxide or hydrogen sulphide is
  formed

184
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
(a)
(b)
Action of concentrated sulphuric(VI) acid on (a)
sodium bromide (b) sodium iodide
185
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.95)
Reactions with ConcentratedSulphuric(VI) Acid

• Bromides
• NaBr(s) H2SO4(l) ?? NaHSO4(s) HBr(g)
• 2HBr(g) H2SO4(l) ?? SO2(g) Br2(g)
  2H2O(l)

186
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• The chemical equation for the overall reaction is
• 2NaBr(s) 3H2SO4(l) ?? 2NaHSO4(s) SO2(g)
  Br2(g) 2H2O(l)

187
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• Iodides
• NaI(s) H2SO4(l) ?? NaHSO4(s) HI(g)
• 8HI(g) H2SO4(l) ?? H2S(g) 4I2(g) 4H2O(l)

188
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• The chemical equation for the overall reaction is
• 8NaI(s) 9H2SO4(l) ?? 8NaHSO4(s) H2S(g)
  4I2(g) 4H2O(l)

189
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• Bromides and iodides
• ? do not react in the same way as fluorides
  and chlorides
• ? the hydrogen bromide and hydrogen iodide
  produced are oxidized by concentrated
  sulphuric(VI) acid to bromine and iodine
  respectively

190
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• Hydrogen chloride
• ? is not oxidized by concentrated
  sulphuric(VI) acid

191
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Action of concentrated sulphuric(VI) acid on
halides
192
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Action of concentrated sulphuric(VI) acid on
halides
193
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Action of concentrated sulphuric(VI) acid on
halides
194
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• The reaction of chlorides with concentrated
  sulphuric(VI) acid
• ? used for the preparation of hydrogen
  chloride in the laboratory

195
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.96)
Reactions with ConcentratedSulphuric(VI) Acid

• Hydrogen bromide and hydrogen iodide
• ? cannot be prepared in this way

196
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.97)
Reactions with Phosphoric(V) Acid

• Phosphoric(V) acid
• ? not an oxidizing agent
• ? reacts with halides to form the
  corresponding hydrogen halides
• ? a general method to prepare hydrogen
  halides in the laboratory

197
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.97)
Reactions with Phosphoric(V) Acid
3NaCl(s) H3PO4(l) ?? Na3PO4(s)
3HCl(g) 3NaBr(s) H3PO4(l) ?? Na3PO4(s)
3HBr(g) 3NaI(s) H3PO4(l) ?? Na3PO4(s)
3HI(g)
198
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.97)
Action of concentrated phosphoric(V) acid on
halides
199
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Introduction

• Hydrogen halides
• ? prepared by the direct reactions of
  hydrogen with halogens

200
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Introduction

• Hydrogen
• ? reacts explosively with fluorine

201
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Introduction

• Hydrogen chloride is formed
• ? when hydrogen burns in chlorine gas

202
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Introduction

• Hydrogen
• ? reacts with bromine or iodine in
  the presence of a catalyst at high
  temperatures
• ? form hydrogen bromide and hydrogen iodide
  respectively
• H2(g) X2(g) ?? 2HX(g)

203
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Introduction

• Hydrogen halides
• ? prepared by adding concentrated phosphoric(V)
  acid to the halides
• 3X(aq) H3PO4(l) ?? PO43(aq) 3HX(g)

204
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Some physical properties of hydrogen halides
205
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Acidic Properties of Hydrogen Halides

• Hydrogen halides
• ? dissociate in water to form acidic solutions

206
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Acidic Properties of Hydrogen Halides

• The larger the acid dissociation constant
• ? the stronger its acid strength

207
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.98)
Acidic Properties of Hydrogen Halides

• The acid strength of hydrogen halides decreases
  in the order
• HI gt HBr gt HCl gtgt HF

208
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
Acid dissociation constants of hydrogen halides
and their degrees of dissociation in 0.1 M
solutions
209
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
Anomalous Behaviour of Hydrogen Fluoride
1. Hydrogen fluoride has abnormally high boiling
point and melting point amongthe hydrogen
halides

• Molecules of all other hydrogen halides
• ? held together by weak van der Waals forces
  only

210
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
Formation of the extensive intermolecular
hydrogen bonds among hydrogen fluoride molecules
211
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
2. Hydrogen fluoride is soluble in water

• A dilute solution of hydrogen fluoride
• ? behaves only as a weak acid

212
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
2. Hydrogen fluoride is soluble in water

• A more concentrated solution of hydrogen fluoride
• ? another equilibrium is established
• ? the fluoride ion form the complex ion HF2

213
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
2. Hydrogen fluoride is soluble in water

• The equilibrium of reaction (2)
• ? shifts to the right
• ? the concentration of hydrogen fluoride
  increases

214
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
2. Hydrogen fluoride is soluble in water

• The consumption of fluoride ions in reaction (2)
• ? the equilibrium of reaction (1) also shifts
  to the right

215
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
2. Hydrogen fluoride is soluble in water

• The acid strength of hydrogen fluoride
• ? enhanced

216
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.99)
2. Hydrogen fluoride is soluble in water

• A concentration of approximately5 to 15 M of
  hydrogen fluoride
• ? effectively a strong acid

217
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.100)
3. Other fluorides (e.g. potassium fluoride) also
react with hydrogen fluoride to form acid salts
containing the stable HF2ion
218
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.100)
3. Other fluorides (e.g. potassium fluoride) also
react with hydrogen fluoride to form acid salts
containing the stable HF2ion

• Heating the solid potassium hydrogen difluoride
• ? reverses the reaction
• ? a convenient way to obtain anhydrous
  hydrogen fluoride

219
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.100)
4. A special property of hydrofluoric acid is its
ability to react with glass

• Use to etch glass

220
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.100)
A glass is etched by hydrofluoric acid
221
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.100)
4. A special property of hydrofluoric acid is its
ability to react with glass

• The glass object to be etched
• ? coated with wax or a similar acid- proof
  material
• ? cutting through the wax layer to expose the
  glass
• ? apply hydrofluoric acid

222
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen Fluoride (SB
p.100)
4. A special property of hydrofluoric acid is its
ability to react with glass

• The principle of etching glass
• CaSiO3(s) 6HF(aq) ?? CaF2(aq) SiF4(aq)
  3H2O(l)

223
The END
224
41.1 Characteristic Properties of the Halogens
(SB p.82)
Let's Think 1
What is the predicted colour of astatine?
Answer
The colour of astatine is black.
Back
225
41.1 Characteristic Properties of the Halogens
(SB p.83)
Check Point 41-1
(a) Write the electronic configuration of each of
the halogens. What is in common about these
electronic configurations?
Answer
226
41.1 Characteristic Properties of the Halogens
(SB p.83)
(a) They have the outermost shell
electronic configuration of ns2np5.
227
41.1 Characteristic Properties of the Halogens
(SB p.83)
Check Point 41-1
(b) Does a halogen atom gain or lose an electron
more readily when forming a compound?
Answer
(b) A halogen atom tends to gain an electron when
forming a compound.
228
41.1 Characteristic Properties of the Halogens
(SB p.83)
Check Point 41-1
(c) The colour of halogens darkens on going down
the group. Explain why.
Answer
(c) Going down the halogen, the sizes of the
halogen atoms increase, and the radiation of
lower frequency is absorbed. For instance, since
fluorine atom has a smaller size, it tends to
absorb the radiation of relatively high frequency
(i.e. blue light), hence fluorine appears yellow.
Atoms of other halogens have larger sizes and
they absorb radiation of lower frequency. For
example, iodine absorbs the radiation of
relatively low frequency (i.e. yellow light),
hence iodine appears violet.
Back
229
41.2 Variation in Properties of the Halogens (SB
p.86)
Check Point 41-2A
(a) Explain the term electron affinity.
Describe the trend of variation in electron
affinity of the halogens.
Answer
230
41.2 Variation in Properties of the Halogens (SB
p.86)
(a) Electron affinity is the enthalpy change when
one mole of electrons is added to one mole of
atoms or ions in the gaseous state. The electron
affinity increases from fluorine to chlorine and
then decreases from chlorine to astatine. The
general decrease in electron affinity is due to
the increases in atomic size and number of
electron shells down the group. This leads to a
decrease in effective nuclear charge. Therefore,
the tendency of the nuclei of halogen atoms to
attract additional electrons decreases. On the
other hand, fluorine has an abnormally low
electron affinity. It is because fluorine atom
has a very small atomic size. Energy is required
to overcome the repulsion between the additional
electron and the electrons present in the
electron shell. The electron affinity of fluorine
is therefore lower than expected.
231
41.2 Variation in Properties of the Halogens (SB
p.86)
Check Point 41-2A
(b) For each of the following physical properties
of the halogens, state the trend down the
group. (i) Atomic radius (ii) Ionic
radius (iii) Melting point (iv) Electronegativit
y (v) Colour intensity
(b) (i) Increase (ii) Increase (iii) Increase (
iv) Decrease (v) Increase
Answer
Back
232
41.2 Variation in Properties of the Halogens (SB
p.90)
Let's Think 2
Why does fluorine always behave differently from
chlorine, bromine and iodine?
Answer
Fluorine cannot expand its octet as there are no
low-lying emptyd orbitals available, and the
energy required to promote electrons into the
third quantum shell is very high. Since fluorine
is the most electronegative element and there is
only one unpaired p electron available for
bonding, its oxidation state is limited to 1
when bonded with other elements.
Back
233
41.2 Variation in Properties of the Halogens (SB
p.91)
Check Point 41-2B
(a) Explain why halogens are strong oxidizing
agents.
Answer
(a) It is because all halogens have one electron
short of the octet electronic configuration, they
tend to attract an additional electron to
complete the octet. They have high
electronegativity values and highly negative
electron affinity values. Halogens are thus
strong oxidizing agents.
234
41.2 Variation in Properties of the Halogens (SB
p.91)
Check Point 41-2B
(b) What chemical species are present in the
following solutions? (i) Chlorine
water (ii) Bromine water (iii) Iodine in
potassium iodide solution
Answer
(b) (i) Cl2(aq), Cl(aq), ClO(aq), H(aq), H2O(l
) (ii) Br2(aq), Br(aq), BrO(aq), H(aq), H2O(l
) (iii) I(aq), K(aq), I3(aq), H2O(l)
Back
235
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Check Point 41-3A
(a) Is bromine and iodine more soluble in water
or 1,1,1-trichloroethane? Explain your answer.
Answer
(a) Both bromine and iodine are more soluble in
1,1,1-trichloroethane than in water. It is
because both bromine and iodine are non polar
molecules, and water is a much polar solvent than
1,1,1-trichloroethane.
236
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.93)
Check Point 41-3A
(b) Describe a simple way to increase the
solubility of iodine in water.
Answer
(b) The solubility of iodine in water can be
increased by adding potassium iodide solution.
Iodine exists as triiodide ions in potassium
iodide solution as shown in the following
equationI2(s) KI(aq) ?? KI3(aq)
Back
237
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.97)
Check Point 41-3B
(a) State any observable changes when the
following substances are added into sodium iodide
solution. Give appropriate equations, if
any. (i) Iron(II) sulphate(VI) solution
Answer
(a) (i) There is no observable change.
238
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.97)
Check Point 41-3B
(a) State any observable changes when the
following substances are added into sodium iodide
solution. Give appropriate equations, if
any. (ii) Chlorine water
Answer
(a) (ii) The solution turns yellowish
brown. Cl2(aq) 2NaI(aq) ?? I2(aq) 2NaCl(aq)
239
41.3 Comparative Study of the Reactions of
Halide Ions (SB p.97)
C