Group IV Elements

1
Group IV Elements
42.1 Introduction 42.2 Characteristic Properties
of the Group IV Elements 42.3 Composition of
Chlorides and Oxides of the Group IV
Elements 42.4 Silicon and Silicates
2
Introduction
3
42.1 Introduction (SB p.106)
Introduction

• The Group IV elements
• ? reveals a marked change among the elements
• ? exhibit considerable change in character
  (or dissimilarity)

4
42.1 Introduction (SB p.106)
Introduction

• The Group IV elements
• ? carbon
• ? silicon
• ? germanium
• ? tin
• ? lead

5
42.1 Introduction (SB p.106)
Introduction

• Carbon
• ? dull black in the form of graphite

6
42.1 Introduction (SB p.106)

• Appearances of the Group IV elements at room
  temperature and pressure carbon (graphite)

7
42.1 Introduction (SB p.106)
Introduction

• Carbon
• ? hard and transparent in the form of diamond

8
42.1 Introduction (SB p.106)

• Appearances of the Group IV elements at room
  temperature and pressure carbon (diamond)

9
42.1 Introduction (SB p.106)
Introduction

• Silicon and germanium
• ? dull grey or black

10
42.1 Introduction (SB p.106)

• Appearances of the Group IV elements at room
  temperature and pressure silicon

11
42.1 Introduction (SB p.106)

• Appearances of the Group IV elements at room
  temperature and pressure germanium

12
42.1 Introduction (SB p.106)
Introduction

• Tin and lead
• ? shiny grey

13
42.1 Introduction (SB p.106)

• Appearances of the Group IV elements at room
  temperature and pressure tin

14
42.1 Introduction (SB p.106)

• Appearances of the Group IV elements at room
  temperature and pressure lead

15
42.1 Introduction (SB p.106)
Introduction

• The Group IV elements
• ? outermost shell electronic configuration of
  ns2np2

16
Electronic configurations of the Group IV elements
42.1 Introduction (SB p.107)
Element Electronic configuration
Carbon He 2s22p2
Silicon Ne 3s23p2
Germanium Ar 3d104s24p2
Tin Kr 4d 105s25p2
Lead Xe 4f 145d 106s26p2
17
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
Structure and Bonding

• Moving down the group
• ? change from non-metal to metal

18
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
Structure and Bonding

• Carbon
• ? non-metal

19
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
Structure and Bonding

• Silicon and germanium
• ? metalloids

20
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
Structure and Bonding

• Tin and lead
• ? typical metals

21
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
Structure and Bonding

• The most common structure in Group IV elements
• ? giant covalent structure

22
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
Structure and Bonding

• Example of giant covalent structure
• ? carbon
• ? silicon
• ? germanium
• ? grey tin (an allotrope of tin)

23
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
1. Carbon

• Carbon
• ? two important allotropic forms
• ? diamond and graphite

24
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
1. Carbon

• Diamond
• ? extended covalently-bonded structure
• ? each carbon atom is bonded to four other
  carbon atoms

25
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
1. Carbon

• This compact and rigid arrangement of carbon
  atoms
• ? extremely hard and chemically inert

26
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)

• Structures of the two allotropic forms of carbon
  diamond

27
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
1. Carbon

• Graphite
• ? layered structure
• ? layers of covalently-bonded carbon atoms
  are held together by weak van der Waals forces

28
42.2 Characteristic Properties of the Group IV
Elements (SB p.107)
1. Carbon

• These layers slide over each other easily
• ? brittle and soft

29
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)

• Structures of the two allotropic forms of carbon
  graphite

30
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
2. Silicon and Germanium

• Silicon and germanium
• ? network lattice
• ? the atoms are covalently bonded to one
  another

31
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
3. Tin and Lead

• Tin
• ? two allotropes
• ? white tin and grey tin

32
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
3. Tin and Lead

• White tin
• ? stable form
• ? metallic lattice structure
• ? atoms are held together by metallic bonding

33
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
3. Tin and Lead

• White tin
• ? conducts electricity
• ? shows the properties of a typical metal

34
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
3. Tin and Lead

• Grey tin
• ? network lattice structure
• ? similar to that of diamond

35
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
3. Tin and Lead

• Lead
• ? typical metallic lattice
• ? atoms are held together by metallic bonding

36
Some physical properties of the Group IV elements
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
Carbon (C) Silicon (Si) Germanium (Ge)
Electronegativity value 2.5 1.74 2.0
Electronic configuration 1s22s22p2 Ne 3s23p2 Ar 4s24p2
Atomic radius (nm) 0.077 0.117 0.122
Bond enthalpy (kJ mol1) 347 226 188
Melting point (?C) 3550 1410 937
Boiling point (?C) 4287 2355 2830
Enthalpy change of atomization (kJ mol1) 716 456 376
37
Some physical properties of the Group IV elements
42.2 Characteristic Properties of the Group IV
Elements (SB p.108)
Tin (Sn) Lead (Pb)
Electronegativity value 1.7 1.55
Electronic configuration Kr 5s25p2 Xe 6s26p2
Atomic radius (nm) 0.140 0.154
Bond enthalpy (kJ mol1) 150
Melting point (?C) 230 327
Boiling point (?C) 2270 1740
Enthalpy change of atomization (kJ mol1) 302 195
38
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• The variation in melting point of the Group IV
  elements

39
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• The melting points
• ? general decrease on going down the group

40
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• The very high melting point of diamond
• ? the great amount of energy needed to break
  the strong C C single bonds

41
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• Going from carbon to germanium
• ? the bond lengths increase
• ? the bond strengths decrease
• ? the lower melting points

42
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• A further and bigger fall to tin
• ? a slight rise to lead

43
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• Tin and lead
• ? metallic structures
• ? no need to break strong metallic bonds to
  bring about melting

44
42.2 Characteristic Properties of the Group IV
Elements (SB p.109)
Variation in Melting Point

• Tin and lead
• ? only two of the four valence electrons are
  delocalized to form metallic bonds
• ? unusually low melting points

45
42.2 Characteristic Properties of the Group IV
Elements (SB p.110)
Variation in Boiling Point

• Variation in boiling point of the Group IV
  elements

46
42.2 Characteristic Properties of the Group IV
Elements (SB p.110)
Variation in Boiling Point

• The general trend and explanation
• ? similar to those for melting point

47
42.2 Characteristic Properties of the Group IV
Elements (SB p.110)
Variation in Boiling Point

• Germanium
• ? abnormally high boiling point
• ? changes to partial metallic structure in the
  liquid state
• ? four valence electrons participate in the
  formation of metallic bonds

48
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.110)
Chlorides

• Two series of chlorides formed by the Group IV
  elements
• ? the dichlorides (MCl2)
• ? the tetrachlorides (MCl4)

49
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.110)
Chlorides

• The Group IV elements
• ? show a trend of dissimilarity

50
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.110)
Chlorides

• Going down the group
• ? an increasing tendency to form dichlorides

51
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• All Group IV elements
• ? form tetrachlorides
• ? liquids at room temperature and pressure
• ? all simple covalent molecules with a
  tetrahedral shape

52
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)

• All tetrachlorides of the Group IV elements have
  a tetrahedral shape

53
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• The bonds formed by the Group IV elements and
  chlorine (M Cl bonds)
• ? covalent
• ? substantial amount of ionic character

54
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Silicon(IV) chloride
• ? more pronounced in than in the
  tetrachlorides of carbon or germanium
• ? silicon has much lower electronegativity
  than carbon or germanium

55
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Each M Cl bond
• ? polar
• ? molecule as a whole
• ? no dipole moments
• ? symmetrical shape

56
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Only germanium, tin and lead
• ? form dichlorides
• ? formulae are GeCl2, SnCl2 and PbCl2
  respectively
• ? all possess covalent character though they
  exist as crystalline solids at room temperature
  and pressure

57
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Germanium(II) chloride and tin(II) chloride
• ? mainly covalent

58
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Lead(II) chloride
• ? mainly ionic

59
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Going down the group, the relative stability
• ? the 4 oxidation state decreases
• ? the 2 oxidation state becomes more stable

60
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Carbon
• ? does not form dichloride

61
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Chlorides

• Lead(II) chloride
• ? more stable than lead(IV) chloride

62
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Oxides

• Two series of oxides formed by the Group IV
  elements
• ? the monoxides (MO)
• ? the dioxides (MO2)

63
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Oxides

• Monoxides
• ? oxidation state of 2

64
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Oxides

• Dioxides
• ? oxidation state of 4

65
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Oxides

• All Group IV elements
• ? form the dioxides

66
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Oxides

• Carbon dioxide
• ? only one which consists of simple molecules
• ? exists as a gas at room temperature and
  pressure

67
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.111)
Oxides

• The dioxides of other Group IV elements
• ? crystalline solids of high melting points
• ? either giant covalent or giant ionic
  structures

68
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Oxides

• All Group IV elements (except silicon)
• ? form the monoxides at normal conditions

69
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Oxides

• Carbon monoxide (CO)
• ? molecular compound

70
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Oxides

• Germanium monoxide (GeO)
• ? black solid
• ? formed by the reduction of germanium
  dioxide (GeO2)

71
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Oxides

• Tin monoxide (SnO) and lead monoxide (PbO)
• ? predominantly ionic solids

72
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Oxides

• Going down the group
• ? a general increase in stability of the
  monoxides relative to the dioxides

73
The bond type and the relative stability of the
monoxides and dioxides formed by the Group IV
elements
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Group IV element Oxides formed Bond type of the oxide Relative stability
Carbon CO Covalent Unstable (reducing)
Carbon CO2 Covalent Stable
Silicon (SiO) Very unstable
Silicon SiO2 Covalent Stable
Germanium GeO Predominantly ionic Unstable in the presence of oxygen
Germanium GeO2 Partly ionic, partly covalent Stable
74
The bond type and the relative stability of the
monoxides and dioxides formed by the Group IV
elements
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Group IV element Oxides formed Bond type of the oxide Relative stability
Tin SnO Predominantly ionic Unstable (reducing)
Tin SnO2 Partly ionic, partly covalent Unstable (oxidizing)
Lead PbO Ionic Stable
Lead PbO2 Predominantly ionic Unstable (oxidizing)
75
42.4 Silicon and Silicates (SB p.113)
Silicon

• Silicon
• ? the second most abundant element in the
  Earths crust
• ? about 28 by mass

76
42.4 Silicon and Silicates (SB p.113)
Silicon

• Silicon
• ? commonly found as silicon oxide (also known
  as silica)

77
42.4 Silicon and Silicates (SB p.113)
Silicon

• Example
• ? in a variety of forms such as sand, quartz
  and flint
• ? also found as silicates in rocks and clay

78
42.4 Silicon and Silicates (SB p.113)
Silicon

• Silicon
• ? can be obtained from silica
• ? by reduction with carbon in an electric
  furnace
• SiO2(s) 2C(s) ?? Si(s) 2CO(g)

79
42.4 Silicon and Silicates (SB p.113)
Silicon

• Extremely pure silicon
• ? can be obtained by the reaction of
  silicon(IV) chloride with hydrogen
• ? followed by zone refining of the resultant
  silicon
• SiCl4(s) 2H2(g) ?? Si(s) 4HCl(l)

80
42.4 Silicon and Silicates (SB p.113)
Silicon

• Silicon is the basic material
• ? for making semi-conductors used in the
  construction of transistors and rectifiers
• ? for making steel and aluminium alloys

81
42.4 Silicon and Silicates (SB p.113)
Silicon

• The chemistry of silicon
• ? dominated by its strong tendency to form Si
  O single bond
• ? reflected by its formation of silica and a
  variety of silicates

82
42.4 Silicon and Silicates (SB p.113)
Structures and Bonding of Silicates
1. SiO44 as the Basic Chemical Unit of Silicates

• Silicates
• ? compounds of silicon, oxygen and one or
  more metals

83
42.4 Silicon and Silicates (SB p.113)
1. SiO44 as the Basic Chemical Unit of Silicates

• Silicates
• ? the largest and the most complicated class
  of minerals
• ? about 30 of all minerals are silicates

84
42.4 Silicon and Silicates (SB p.113)
1. SiO44 as the Basic Chemical Unit of Silicates

• The basic chemical unit of silicates
• ? the SiO44 anion
• ? tetrahedral shape

85
42.4 Silicon and Silicates (SB p.113)

• The basic chemical unit of silicates the SiO44
  anion

86
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• In the SiO44 anion
• ? formed its maximum number of bonds (i.e. 4)

87
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• Each oxygen atom
• ? located at the corner of the tetrahedron
• ? forms only one single bond
• ? gain an extra electron in order to achieve
  the stable octet electronic configuration

88
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• The oxygen atom also
• ? form one more single bond
• ? carry no electric charge

89
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• A few silicate minerals
• ? contain SiO44 as discrete ions
• ? known as orthosilicates

90
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• Zircon (ZrSiO4)
• ? example of such a silicate mineral
• ? the principal ore of zirconium metal

91
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• Zircon (ZrSiO4)
• ? brilliant appearance
• ? high refractive index
• ? used as a diamond-like gem

92
42.4 Silicon and Silicates (SB p.114)

• Zircon is used as a diamond-like gem

93
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• Most silicate minerals
• ? more complicated structures
• ? SiO44 tetrahedra are linked to other SiO44
  tetrahedra through common oxygen atoms

94
42.4 Silicon and Silicates (SB p.114)

• The Si2O76 anion is formed by joining two SiO44
  tetrahedra together through a common oxygen atom
  (Note that the negative charges are present only
  on the oxygen atoms that are not shared by the
  two silicon atoms)

95
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• The negative charges
• ? present on the oxygen atoms
• ? not shared by the two silicon atoms
• ? balanced by the presence of metal ions in
  the silicate minerals

96
42.4 Silicon and Silicates (SB p.114)
1. SiO44 as the Basic Chemical Unit of Silicates

• In some silicate minerals
• ? the SiO44 tetrahedra are linked to form
  anions that are long chains or sheets

97
42.4 Silicon and Silicates (SB p.115)
2. Structures of Silicates

• The SiO44 tetrahedra can be joined up
• ? by sharing oxygen atoms
• ? form chain, sheet or network silicates

98
42.4 Silicon and Silicates (SB p.115)
Chain silicates

• Two oxygen atoms of an SiO44 tetrahedra are
  shared with other SiO44 tetrahedra
• ? form a ring or an infinite chain

99
42.4 Silicon and Silicates (SB p.115)

• Structure of chain silicate anions

100
42.4 Silicon and Silicates (SB p.115)
Chain silicates

• The stoichiometry of the silicate anion
• ? (SiO3)n2n

101
42.4 Silicon and Silicates (SB p.115)
Chain silicates

• Examples
• ? pyroxene
• ? dark mineral
• ? commonly found in igneous rocks

102
42.4 Silicon and Silicates (SB p.115)
Chain silicates

• Chain silicates
• ? tend to have two directions of cleavage
• ? the individual chains of tetrahedra can be
  separated much more easily

103
42.4 Silicon and Silicates (SB p.115)
Chain silicates

• Some asbestos
• ? long-chain silicate anions present

104
42.4 Silicon and Silicates (SB p.115)

• Chain silicate anions are found in fibrous
  asbestos

105
42.4 Silicon and Silicates (SB p.115)
Sheet silicates

• Each SiO44 tetrahedron
• ? shares three oxygen atoms with neighbouring
  SiO44 tetrahedra
• ? sheet silicates are formed

106
42.4 Silicon and Silicates (SB p.115)

• Structure of sheet silicate anions

107
42.4 Silicon and Silicates (SB p.116)
Sheet silicates

• Sheet silicate anions
• ? found in mica and clay

108
42.4 Silicon and Silicates (SB p.116)

• Sheet silicate anions are found in mica

109
42.4 Silicon and Silicates (SB p.116)

• Sheet silicate anions are found in clay

110
42.4 Silicon and Silicates (SB p.116)
Sheet silicates

• Only weak van der Waals forces exist between the
  sheets of the SiO44 anions
• ? mica and clay readily cleave into thin slices

111
42.4 Silicon and Silicates (SB p.116)
Network silicates

• The mineral quartz
• ? consists of SiO44 tetrahedra
• ? every oxygen is shared with adjacent SiO44
  tetrahedra

112
42.4 Silicon and Silicates (SB p.116)

• Appearance of quartz

113
42.4 Silicon and Silicates (SB p.116)
Network silicates

• In the quartz lattice
• ? each silicon atom is bonded tetrahedrally
  to four neighbouring oxygen atoms
• ? each oxygen atom is bonded to two
  neighbouring silicon atoms

114
42.4 Silicon and Silicates (SB p.116)
Network silicates

• This arrangement
• ? goes on continuously
• ? give a three dimensional network
• ? called network silicate

115
42.4 Silicon and Silicates (SB p.116)

• Structure of quartz (silicon(IV) oxide, SiO2)

116
42.4 Silicon and Silicates (SB p.116)
Network silicates

• Another group of network silicates
• ? the feldspar group

117
42.4 Silicon and Silicates (SB p.116)
Network silicates

• Feldspar
• ? the most abundant group of minerals in the
  Earths crust

118
42.4 Silicon and Silicates (SB p.116)
Network silicates

• In the feldspar structure
• ? every oxygen atom is shared between SiO44
  tetrahedra
• ? some of the tetrahedra have aluminium at
  their centres instead of silicon

119
42.4 Silicon and Silicates (SB p.116)
Network silicates

• Aluminium
• ? one electron less to share than silicon
  atom
• ? allows the oxygen atoms to bond to atoms of
  sodium, potassium or calcium

120
The END
121
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Let's Think 1
What is/are the oxidation state(s) of lead in
Pb3O4?
Answer
Pb3O4 is a mixed oxide (PbO2 and 2PbO). The
oxidation states of lead are 4 and 2 in the
mixed oxide Pb3O4.
Back
122
42.3 Composition of Chlorides and Oxides of the
Group IV Elements characteristic (SB p.112)
Check Point 42-3
Why does carbon dioxide exist as a gas while the
dioxides of the other Group IV elements exist as
solids of high melting points at room temperature
and pressure?
Answer
Carbon dioxide is a molecular compound. The
carbon dioxide molecules are only held together
by weak van der Waals forces. This results in
its low melting point. In contrast, the dioxides
of other Group IV elements have either giant
covalent structure or giant ionic structure. As a
result, strong covalent bonds or ionic bonds have
to be broken in the process of melting of these
compounds. Therefore, they have relatively high
melting points.
Back
123
42.4 Silicon and Silicates (SB p.116)
Let's Think 2
What is the chemical formula of the sheet
silicate anion?
Answer
Si4O104
Back