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9
3 Chemical Bonding
This topic introduces the different ways by which chemical bonding occurs and the
effect this can have on physical properties.
3.1 Ionic Bonding
3.4 Metallic Bonding
3.5 Bonding and physical properties
BONDING: OTHER
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Cambridge
as simple International
examples: AS andCO
BF3 (trigonal), A Level Chemistry 9701 syllabus Syllabus content
2 (linear), CH4 (tetrahedral), NH3
(pyramidal), H2O (non-linear), SF6 (octahedral), PF5 (trigonal bipyramidal)
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d) predict the shapes of, and bond angles in, molecules and ions analogous
to those specified 10
in 3.2(b) (see also Section 14.3)
3.3Chemical
3 Intermolecular
bonding a) describe hydrogen bonding, using ammonia and water as simple
forces,
This topic introduces the differentexamples
ways by of molecules
which chemical containing
bonding N–H andand
occurs O–Hthegroups
effect this can have
electronegativity
on physical properties. b) understand, in simple terms, the concept of electronegativity and apply
and bond properties
it to explain the properties of molecules such as bond polarity (see
also Section
Learning outcomes3.3(c)), the dipole moments of molecules (3.3(d)) and the
behaviour
Candidates of oxides
should be ablewith
to:water (9.2(c))
c) explain the terms bond energy, bond length and bond polarity and use
3.1 Ionic bonding them to compare the reactivities of covalent bonds (see also Section
a) describe ionic bonding, as in sodium chloride, magnesium oxide and
5.1(b)(ii))
calcium fluoride, including the use of ‘dot-and-cross’ diagrams
d) describe intermolecular forces (van der Waals’ forces), based on
permanent and induced dipoles, as in, for example, CHCl 3(l); Br2(l) and
3.2 Covalent bonding a) describe,
the liquid including
Group 18 the use of ‘dot-and-cross’ diagrams:
elements
and co-ordinate
(i) covalent bonding, in molecules such as hydrogen, oxygen, chlorine,
(dative covalent)
3.4 bonding
Metallic bonding hydrogen chloride, carbon dioxide, methane, ethene
including a) describe metallic bonding in terms of a lattice of positive ions
shapes of simple (ii) co-ordinate
surrounded (dative covalent)
by delocalised bonding, such as in the formation of the
electrons
molecules ammonium ion and in the Al 2Cl 6 molecule
3.5 Bonding and b) describe covalent bonding in terms of orbital overlap, giving σ and π
a) describe, interpret and predict the effect of different types of bonding
physical properties bonds, including the concept of hybridisation to form sp, sp2 and sp3
(ionic bonding, covalent bonding, hydrogen bonding, other intermolecular
orbitals (see also Section 14.3)
interactions, metallic bonding) on the physical properties of substances
c) explain the shapes of, and bond angles in, molecules by using the
b) deduce the type of bonding present from given information
qualitative model of electron-pair repulsion (including lone pairs), using
c) as
show understanding
simple examples: BFof chemical reactions in terms of energy transfers
3 (trigonal), CO2 (linear), CH4 (tetrahedral), NH3
associated with the breaking and making of chemical
(pyramidal), H2O (non-linear), SF6 (octahedral), bondsbipyramidal)
PF5 (trigonal
d) predict the shapes of, and bond angles in, molecules and ions analogous
to those specified in 3.2(b) (see also Section 14.3)
Back to contents page
3.3 Intermolecular a) describe hydrogen bonding, using ammonia and waterwww.cie.org.uk/alevel
as simple 19
forces, examples of molecules containing N–H and O–H groups
electronegativity
b) understand, in simple terms, the concept of electronegativity and apply
and bond properties
it to explain the properties of molecules such as bond polarity (see
also Section 3.3(c)), the dipole moments of molecules (3.3(d)) and the
behaviour of oxides with water (9.2(c))
c) explain the terms bond energy, bond length and bond polarity and use
them to compare the reactivities of covalent bonds (see also Section
5.1(b)(ii))
d) describe intermolecular forces (van der Waals’ forces), based on
permanent and induced dipoles, as in, for example, CHCl 3(l); Br2(l) and
the liquid Group 18 elements
3.4 Metallic bonding a) describe metallic bonding in terms of a lattice of positive ions
surrounded by delocalised electrons
3.5 Bonding and a) describe, interpret and predict the effect of different types of bonding
physical properties (ionic bonding, covalent bonding, hydrogen bonding, other intermolecular
interactions, metallic bonding) on the physical properties of substances
b) deduce the type of bonding present from given information
c) show understanding of chemical reactions in terms of energy transfers
associated with the breaking and making of chemical bonds
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nding The strong force of attraction between the oppositely
IONIC BONDING
charged positive and negative ions results in an
med? ionic bond. An ionic bond is sometimes called an
atoms lose or gain electrons. Ionic bondingelectrovalent
involvesbond. In an ionic
a transfer ofstructure,
one or the
moreionselectrons
are from one atom to
med when an atom loses oneanother, or arranged in a regular repeating pattern (see Chapter 5).
leading to the formation of an ionic bond.
As a result of this, the force between one ion and the ions
al atoms usually lose electrons and
of opposite charge which surround it is very great. In
The strongotherelectrostatic attraction that prevails between the oppositely
words, ionic bonding is very strong.
med when an atom gains one or
charged ions in a crystal lattice is referred to as ionic bonding.
-metal atoms usually gain electrons
ns. Dot-and-cross diagrams
depends on the number ofPositive ions, Youknown
will noticeasthat in Figureare
cations, we used dots
4.2, formed and electrons are removed from
when
d (see page 29). crosses to show the electronic configuration of the chloride
ne with non-metals, the electrons
atoms. They are smaller than the original atom. The energy associated with the
and sodium ions. This helps us keep track of where the
e metal atoms are transferred process
to is known as the
electrons have come ionisation
from. It doesenergy
not mean that the
Each non-metal atom usually gains electron transferred is any different from the others.
l its outer shell. As a result ofNegative
this, ions, known
Diagrams as are
like this anions, are larger than
called dot-and-cross the original atom. Energy is
diagrams.
tal atoms usually end up with outer as the
released When drawing apulls
nucleus dot-and-cross diagram forThis
in an electron. an ionic
energy is the electron affinity.
re complete – they have an electron compound it is usually acceptable to draw the outer
2+ 2–
ble gas. electron shell of the metal ion without any electrons. This
n see that: is because it has transferred these Oelectrons
1 to the negative
Mg O
Mg
he electronic structure [2,8]+, the ion. Figure 4.4 shows the outer shell dot-and-cross 2+ 2–
diagram for sodium chloride.
2+ 2–
the electronic structure [2,8,8]−, the A dot-and-cross2,8,2
diagram shows:
Mg 2,6
O [2,8]
Mg [2,8]
O
n. • the outer electron shells only MgO
• that the charge of the ion is spread evenly, by using 2+
Figure2,8,2 [2,8] oxide. [2,8]2–
2,6diagram for magnesium
4.5 Dot-and-cross
square brackets
MgO
• the charge on each ion, written at the top right-hand
corner of the square brackets.
a noble gas electron configuration Calcium
Figure 4.5 chloride
Dot-and-cross diagram for magnesium oxide.
the German physicist Walther Kossel Each calcium atom has two electrons in its outer shell and
ar the American chemist Gilbert Lewis
idea independently. ‘DOTthese AND
Calciumcanchloride CROSS’
be transferred DIAGRAMS
to two chlorine atoms. By losing
two
Each calcium atom has two electrons in itsthe
electrons, each calcium atom achieves electron
outer shell and
confi
theseguration [2,8,8] (Figure
can be transferred 4.6).
to two The two
chlorine chlorine
atoms. By losing
tals of salt are made up of millions of sodium ions atoms each gaineach
two electrons,
NaCl
onecalcium
electronatom
to achieve thethe
achieves
MgO
electron
electron
confi guration [2,8,8].
+configuration [2,8,8]–
[2,8,8] is the electron confi
(Figure 4.6). The two chlorine
2+ guration2–
tals of salt are made up of millions of sodium ions
of argon; it is a ‘noble-gas confi guration’.
atoms each gain one electron to achieve the electron
Na Cl Na Mg Cl
configuration O
[2,8,8]. Mgelectron confiO
[2,8,8] is the guration
+ – of argon; it is a ‘noble-gas configuration’. –
2,8,1 2,8,7 [2,8]xx
+
x [2,8,8] – [2,8]2+ [2,8]2–
x NaClx 2,8,2 2,6
[ x Na x]+(Na [Cl )Cl ]–
+ –
Cl CaCl2
MgO Cl
a + Cl – xx
2+ –
f a sodium ion and chloride ion by electron transfer.
Figure 4.5 Dot-and-cross diagram for magnesium oxide. [2,8,8] –
Ca 2,8,7
Cl Ca Cl
a Cl 2+ –
oss diagram for sodium chloride. [2,8,8] –
Calcium chloride
Ca 2,8,7
Cl Ca 2+
[2,8,8]
Cl
2,8,8,2 –
Each calcium atom has two electrons in its outer shell and
ross diagram for sodium chloride. these can be transferred Cl to2 two chlorine atoms. By
2,8,7 Cl – losing
[2,8,8]
sg of dot-and-cross diagrams 2,8,8,2 [2,8,8]2+ CaCl2
two electrons, each calcium atom achieves the electron
e confiFigure
guration [2,8,8]2,8,7
(Figure
4.6 Dot-and-cross 4.6).
diagram for Thchloride.
calcium e two chlorine
[2,8,8] –
es made
of dot-and-cross
up of millions ofdiagrams
m reacts with oxygen tosodium
form ions atoms each gain one electron to achieve the2 electron CaCl
e the two electrons in the outer shell of
atom arewith
transferred
configuration [2,8,8]. [2,8,8]
Figure 4.6 Dot-and-cross diagram is
for the electron
calcium chloride.configuration
m reacts oxygento tothe
formincompletely Check-up
of argon; it is a ‘noble-gas configuration’.
enthe
oxygen atom. Byin
two electrons losing two electrons,
the outer shell of
atom CEDAR
atom achieves the electron
to theconfi guration
COLLEGE 1 Draw dot-and-cross diagrams for the BONDING: OTHER
are transferred incompletely Check-up
.nBy gaining
oxygen twoBy
atom. electrons, eachelectrons,
losing– two following ionic compounds. Show only the
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eves the electron configuration [2,8]. –
outer electron shells.
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SKILL CHECK
(a) Define ionic bonding.
(b) Explain in terms of electrons, how an ionic bond forms between
atoms of calcium and atoms of fluorine.
(c) Draw electron configuration diagrams for a calcium ion and for a
fluoride ion, showing their charges and outer electrons.
3
SKILL CHECK
Draw ‘dot-and-cross’ diagrams for:
(a) lithium fluoride
(b) magnesium chloride
(c) lithium oxide
(d) calcium oxide
4
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SKILL CHECK
In a historically famous experiment Wohler heated “inorganic” ammonium
cyanate in the absence of air. The only product of the reaction was
“organic” urea, CO(NH2)2. No other products were formed in the reaction.
What is the formula of the cyanate ion present in ammonium cyanate?
A CNO- B CNO2- C CO- D NO-
5
IONIC COMPOUNDS
The compounds formed by ionic bonds do not contain individual
molecules, but are formed of an infinite assembly of ions.
The ions due to their mutual attraction arrange themselves in a regular
pattern. Thus they are always crystalline solids at room temperature.
The electrical force binding them being very strong, they are non–volatile
with high melting and boiling points. Every bond in the lattice needs to be
broken down to melt the ionic compound.
6
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IONIC COMPOUNDS
Because they comprised of ions they conduct electricity in the molten or
aqueous state, once the ions are made mobile.
In the solid state they do not conduct electricity. Generally ionic
compounds are soluble in polar solvents likeRelate
water.trends in the properties
of the chlorides of period 3
elements to their structure and
hows some data for some of the chlorides of period 3 elements. bonding
d magnesium chloride are both high-melting-point ionic Describe the reactions of period
y consist of a giant lattice of positive and negative ions (Figure 3 chlorides with water
oppositely charged ions attract each with strong electrostatic
therefore a lot of energy is required to separate the ions. The
these compounds is considered on pages 84–90.
NaCl or MgCl2 are melted, the ions become free to move
7
d so the molten salts conduct electricity.
* **
IONIC LATTICE
Oppositely charged ions held in a regular 3-dimensional lattice by
electrostatic attraction
bonding in the solid state is more ionic with six coordinate Al
valent molecular (Al2Cl6) is present in liquid and gaseous states.
ists as [PCl6]−[PCl4]+ in the solid state but is covalent
n the liquid state.
ding in aluminium chloride is complicated, and it undergoes
structure and bonding as it changes state. For simplicity, we
that the bonding is covalent molecular in all states. The Lewis
r AlCl3 shows that the Al only has six electrons in its outer shell. 8
to generate an octet, two AlCl3 molecules come together to
er. A dative covalent bond is formed from a lone pair on a Cl
CEDAR
ne AlCl3 unit COLLEGE
to an Al on the other AlCl3 unit. BONDING: OTHER
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IONIC LATTICE
Each Na+ is surrounded by 6 Cl¯ Each Cl¯ is surrounded by 6 Na+
Na+ Sodium ion Cl Chloride ion
9
BRITTLE IONIC LATTICES
Ionic compounds are hard. However they are brittle. With a slight
deforming force it is possible to slightly displace one layer of ions relative
to the next and thereby bring ions of similar charge next to each other.
Similar ions repel each other forcing apart the two portions of the crystal.
− + − + − + − +
+ − + − + − + −
If you move a layer of ions, you get ions of the same charge next to each
other. The laters repel each other and the crystal breaks up
10
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SKILL CHECK
Magnesium oxide may be used for the lining of an electric furnace for
making crockery. Which properties of magnesium oxide help to explain
this use?
strong forces between electrical
ionic bonding
particles conductor
A yes yes no
B yes no yes
C no yes no
D no no yes
11
METALLIC BONDING
Involves a lattice of positive ions surrounded by delocalised electrons
Metal atoms achieve stability by “off-loading” outer shell electrons to
attain the electronic structure of the nearest noble gas. These electrons
join up to form a mobile cloud which prevents the newly-formed positive
ions from flying apart due to repulsion between similar charges.
Metals are excellent conductors of
electricity because the ELECTRON CLOUD
IS MOBILE, electrons are free to move
throughout its structure. Electrons attracted
to the positive end are replaced by those
entering from the negative end.
12
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ween the positive metal ions and the negatively charged
17
ons. Each electron is attracted by all the positive ions in
s the whole lattice is held together. The structure of a metal is shown in Figure 3.111.
oints of sodium and magnesium are compared below:
METALLIC BOND STRENGTH
The strength of the metallic bonding in sodium is relatively weak
Metallic bonding is the
because each atom donates one electron to the cloud. The
electrostatic attraction between M
metallic bonding in potassium is weaker than in sodium because Figure
the positive ions in the lattice and 5.9 Youar
io
the resulting ion is larger and the electron cloud has a bigger
the delocalised electrons. this metal plate
de
Figure 5.7 Sapphires sparkle in the light when polished. They
reasons why magnesium
volume has a higher
to cover so ismelting pointatthan
less effective holding the ions together.
are cut by exerting a force on the cleavage planes between M
of these is that magnesium forms a 2+ ion compared lo
layers of ions in the crystal. p
ch forms a 1+ ion.The metallic
This meansbonding
that theinelectrostatic
magnesium is
Alloys andn
n the ions and thestronger thanelectrons
delocalised in sodium is because
stronger each
in
An alloy is a m
The electrons are described as delocalised, because they do not belong
Metallic lattices
atom has donated two electrons to the to any one metal atom, but rather are able to move throughout the
the attraction between the positive metal ions andwith a charged
non-me
structure. The metallic bond is thus electrostatic in nature, resulting from
ason why magnesiumcloud.
hasThe greater
a higher the electron
melting point density
than the negatively
In
theChapter 4, weinlearnt that a metallic latticetheThestructure;
consists oflattice is held together.becomes part o
delocalised electrons. Each electron is attracted by all the positive ions in
ere are two delocalised
holdselectrons per atom
ions together more magnesium;
strongly. thus the whole
melting points of sodium and magnesium are compared below:
ill be a greater number ions surrounded
of electrostatic by a sea of electrons. The ions are often
attractions Brass is anM
packed in hexagonal layers or in
and the delocalised electrons.
13
a cubic arrangement. It is stronger th el
th
2+ +
on is that the Mg ion When
(65 pm) aisforce
smalleristhan
applied,
the Nathe layers can slideThere
over each
are several
reasons
reasons why magnesium has a higher melting point than
it is
th
us
sodium. The first of these is that magnesium forms a 2+ ion compared
therefore the delocalisedother.
electrons
Butare
incloser to the bond, the attractive with
a metallic forces between household item
sodium, which forms a 1+ ion. This means that the electrostatic
attraction between the ions and the delocalised electrons is stronger in
sitive ion in magnesium and more strongly attracted. magnesium.
the metal ions and the delocalised electronssodium, act
The secondinreason
allwhy magnesium has a higher meltingBut why is
point than
is that there are two delocalised electrons per atom in magnesium;
directions. So when the layers slide, new metallic bonds Zinc ions a
therefore there will be a greater number of electrostatic attractions
between the ions and the delocalised electrons.
are easily re-formed between ions in new lattice ion (98 pm),positions
2+ +
The third reason is that the Mg ion (65 pm) is smaller than the Na
ofare closer
and therefore the delocalised electrons different-siz
to the
nucleus of the positive ion in magnesium and more strongly attracted.
and the delocalised electrons (Figure 5.8). The delocalised the lattice less
electrons continue to hold the ions in the lattice together. sliding over ea
METALLIC BONDING
The metal now has a different shape. This explains why (Figure 5.10).
metals
When forceare malleable
is applied, (they
layers can
can be over
slide hammered into different
one another, since attractive
shapes)
forces and metal
between ductileions
(they
andcan
seabeof drawn into
electrons wires).direction,
in every The new force
high bonds
metallic tensileare
strength and hardness
easily re-formed, of most
attaining metalsshape.
a different is alsoThis
due metals
makes to the strong attractive
malleable forces between the metal ions
and ductile.
and the delocalised electrons.
– – – –
+ + + + + + +
+ + + + + force
– – – – –– – – – – ––
force + + + + + + + + + + + +
applied + + + + + + – – –
+ + + + + +
– – – – – – – – –
+ + + + + + + + + +
– – – – – – –
Figure 5.10 Th
Figure 5.8 When a force is applied14 to a metallic structure, than in a pure m
the layers slide over each other and re-form in new lattice less regular.
positions.
Pure aluminiu
thermal condu
aluminium is
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can be increas
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copper, magnethe strength of the intermolecular bonding. The same is true
ble 4.2).
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18
solid argon – weak
instantaneous
dipole forces
SIMPLE MOLECULAR LATTICE
Iodine also forms crystals with
+ +
weak van der Waals’ forces
– – –
+
–
solid iodine – strong
between molecules.
+ + instantaneous
– –
dipole forces This lattice is easily broken
down when iodine is heated.
ula Main type of intermolecular Melting point/∞C
attraction
15
weak instantaneous dipole −189
dipole–dipole −115
hydrogen bonding 0
strong instantaneous dipole 114
2O11 strong hydrogen bonding 185
are in several ways rather different from those of other
nces. Unlike the molecules of other compounds capable of
, water has two lone pairs of electrons together with two
GIANT (MACRO) MOLECULES
means that it can form two hydrogen bonds per molecule
ohols, ammonia and hydrogen fluoride can only form one
Many atoms joined together in a regular array by a large number of
covalent bonds, e.g. diamond, graphite, silicon (iv) oxide.
MELTING POINT ‣ Very high
‣ structure is made up of a large number of covalent bonds, all of
which need to be broken if atoms are to be separated
06/11/14 3:00 PM
ELECTRICAL ‣ Don’t conduct electricity - have no mobile ions or electrons
CONDUCTIVITY ‣ but... Graphite conducts electricity
STRENGTH ‣ Hard - exists in a rigid tetrahedral structure, Diamond and silica
(SiO2)...
‣ but Graphite is soft
16
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DIAMOND
MELTING POINT ‣ VERY HIGH
‣ many covalent bonds must be broken to separate atoms
ELECTRICAL ‣ NON-CONDUCTOR
CONDUCTIVITY ‣ No free electrons - all 4 carbon electrons used for bonding
STRENGTH ‣ STRONG
‣ each carbon is joined to four others in a rigid structure
naturally
lso has
ductivity
than five
th these
le for use
ncrusted
l through
17
Diamond has a very high melting point and boiling point (about
ctures are 4000 °C) because covalent bonds must be broken when diamond is
solids. melted/boiled. Diamond is very hard for the same reason.
Diamond does not conduct electricity, because all the electrons are held
strongly in covalent bonds and are therefore not free to move around in
the structure.
Diamond is not soluble in water or organic solvents, as the forces
between the atoms are too strong. The energy to break these covalent
bonds would not be paid back when the C atoms were solvated.
Like diamond, graphite has a giant covalent structure. Unlike diamond,
however, it has a layer structure (Figure 3.109). Each C is covalently
SILICA
bonded to three others in a trigonal planar array.
MELTING POINT ‣ VERY HIGH
‣ many covalent bonds must be broken
to separate atoms
ELECTRICAL ‣ NON-CONDUCTOR
CONDUCTIVITY ‣ No free electrons
STRENGTH ‣ STRONG
‣ each silicon atom is joined to four
oxygens
‣ each oxygen atom are joined to two
silicons
18
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GRAPHITE
MELTING POINT ‣ VERY HIGH
naturally ‣ many covalent bonds must be broken to separate atoms
so has
ductivity ‣
ELECTRICAL CONDUCTOR
than five
CONDUCTIVITY ‣ Only three carbon electrons are used for bonding which leaves the
h these
e for use
fourth to move freely along layers
ncrusted ‣
STRENGTH SOFT
through
‣ each carbon is joined to three others in a layered structure
‣ layers are held by weak van der Waals’ forces
‣ can slide over each other
Layers can slide over each other
Used as a lubricant and in pencils
Diamond has a very high melting point and boiling point (about
ctures are 4000 °C) because covalent bonds must be broken when 19
diamond is
solids. melted/boiled. Diamond is very hard for the same reason.
Diamond does not conduct electricity, because all the electrons are held
strongly in covalent bonds and are therefore not free to move around in
the structure.
Diamond is not soluble in water or organic solvents, as the forces There are covalent bonds between the C atoms within a layer but only
between the atoms are too strong. The energy to break these covalentvan der Waals’ forces between the layers (some of these are shown in blue
The lubricant propertie
in Figure 3.109). The presence of weak forces between the layers is usually
bonds would not be paid back when the C atoms were solvated. given as the explanation that graphite is a good lubricant (used in pencils, are usually explained as
to the weak forces betw
for example) – not much force is required to separate the layers. However,
of carbon atoms. Howev
it has a very high melting/boiling point, because covalent bonds within
is a poor lubricant in a v
Like diamond, graphite has a giant covalent structure. Unlike diamond,
the layers must be broken when it is melted/boiled.
it is now believed that t
Because of the strong covalent bonds between atoms, graphite is not properties come from ad
however, it has a layer structure (Figure 3.109). Each C is covalently
bonded to three others in a trigonal planar array.
GRAPHITE soluble in water or non-polar solvents.
Graphite conducts electricity because each C atom forms only three
molecules.
covalent bonds, and the extra electrons not used in these bonds (carbon
has four outer shell electrons) are able to move within the layers.
As only three covalent bonds are formed by each carbon atom in the
layers, each C atom possesses one p orbital, containing one electron,
perpendicular to the plane of the layers. These p orbitals can overlap
side on to give a delocalised system extending over the whole layer.
Movement of electrons within this system allows conduction of electricity
within layers. Graphite is, however, an electrical insulator perpendicular to
the plane of the layers.
The third allotrope of carbon that will be considered here is a molecular
rather than a giant structure. It consists of individual C60 molecules, with
covalent bonds within the molecule and van der Waals’ forces between the
molecules (Figure 3.110).
Diamond and graph
20 structures but fullere
molecular structure
points of diamond a
therefore substantiall
that of fullerene, as c
must be broken whe
and graphite are me
intermolecular force
Waals’ forces) when
(it actually undergoe
at about 530 °C).
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CARBON NANOPARTICLES
Cambridge International AS Level Chemistry
Allotropes of carbon, known as fullerenes, have been recently
discovered and possess unique and exciting properties.
They are based on rings of carbon, in hexagonal arrangement, similar to
colourless crystals with high melting and boiling points
the structure of graphite. Fullerenes
and it does not conduct electricity. Fullerenes are allotropes of carbon in t
Sand is They
largelyhave
silicon(IV)oxide.
dimensions between 0.1 to 100 nanometers.
spheres or tubes. They are similar in st
in that each carbon atom is bonded to
QUESTIONS atoms. They contain rings of carbon at
in hexagons and in addition many con
11 Explain the following properties of silicon(IV) oxide by carbon atoms arranged in pentagons. Th
referring to its structure and bonding. discovered was called buckminsterful
a It has a high melting point. 21
5.16). The C60 molecule has the shape o
b It does not conduct electricity. ball). The carbon atoms are arranged a
c It is a crystalline solid. 20 hexagons and 12 pentagons. The bo
d It is hard. hexagons join are shorter than the bon
12 Copy and complete the table below to compare hexagons and the pentagons. As in gra
the properties of giant ionic, giant molecular, giant electrons in C60 are delocalised, but to
metallic and simple molecular structures. in graphite. Since the discovery of the
types of buckminsterfullerene have be
Giant Giant Metallic Simple
FULLERENES are ball-shaped molecules that are mul
ionic molecular molecular
C120. Other fullerene molecules includ
Two The firsts fullerene discovered was the buckminsterfullerene, C60, which has the
examples
shape of a football. a b
Particles
Properties:
present
Forces
Relatively low sublimation point (weak van der
keeping
82 Waals between each molecule).
particles
together
Poor conductor of electricity (extent of electron
Physical
statedelocalisation
at room is lower).
temperature
More reactive compared to graphite. Reacts with
Melting
hydrogen,
points and fluorine, chlorine, bromine and
boiling points Figure Buckminsterfullerene
5.16 The shape of a buckminster
oxygen. C60, a is similar to that of a football b.
Hardness
22
Electrical
conductivity The properties of buckminsterfulleren
Solubility in different from those of graphite and di
water It has a relatively low sublimation poin
■
from the solid to the vapour state whe
CEDAR COLLEGE 600 °C. (Graphite
BONDING:only OTHER
turns from the s
state at about 3700 °C). This is because
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high electron density in certain parts of the molecule (see Graphene
electrophilic addition on page 209).
Graphene is a single iso
A second type of fullerene is a class of molecules described The hexagonally arrang
NANOTUBES as nanotubes. Nanotubes are fullerenes of hexagonally
arranged carbon atoms like a single layer of graphite
completely rigid and it
bent into the form of a cylinder (Figure 5.17). The first a
nanotubes to be made were one layer of carbon atoms in
Nanotubes are fullerenes hexagonally arranged carbon atoms like a single
thickness. More recently nanotubes have behave been made
with thicker walls with several tubes inside one another.
layer of graphite bent into a cylinder. Although the diameter of a nanotube is very small, it
can be made relatively long. The length of the nanotube
cylinder can be a million times greater than its diameter.
Properties:
High electrical conductivity along axis of cylinder. Figure 5.18 a Part of a
of graphene.
High tensile strength. Graphene has some of t
are more exaggerated. F
Very high melting points ( 3500°C). ■ Graphene is the most
Single sheets of graph
and are much more re
Used in tiny electrical circuits as wires, as electrodes ■ Graphene is extremel
■ For a given amount of
in paper thin batteries, treatment of certain types of Figure 5.17 Part of the structure of a nanotube. The ends of
electricity and heat m
the cylinder are often closed. It has been said that ‘a o
cancer in drug delivery and to strengthen clothing. of graphene could supp
Nanotubes have characteristic properties: only as much as the cat
23 of graphene include use
■ They have high electrical conductivity along the long axis
tiny transistors, touchsc
of the cylinder. This is because, like graphite, some of the
electrons are delocalised and are able to move along the
storage devices.
cylinder when a voltage is applied.
■ They have a very high tensile strength when a force is QUESTION
applied along the long axis of the cylinder. They can be up to
100 times stronger than steel of the same thickness. 13 Suggest, using ide
■ They have very high melting points (typically about 3500 °C). a buckminsterfu
This is because there is strong covalent bonding throughout solid to a gas a
the structure.
b graphene is a g
Fullerenes have a large range of potential uses. c nanotubes con
Reactive groups can be attached to their surfaces and long axis of the
metal complexes (see page 371) can also be formed. d buckminsterfu
Small molecules or atoms can be trapped in the cage
of buckminsterfullerenes. Possible medical uses
GRAPHENE include delivering drugs to specific places in the body.
Conserving m
Nanotubes are used in tiny electrical circuits as ‘wires’
and as electrodes in paper-thin batteries. They can be Why conserve m
Single isolated layer of graphite. incorporated into clothing and sports equipment for added There is only a limited s
strength. They have also been used in the treatment of If we use them all up, th
certain types of cancer. we make from metals a
Not completely rigid and shape can be distorted.
Most reactive form of carbon (low melting point).
Extremely strong.
Conducts electricity.
24
CEDAR COLLEGE BONDING: OTHER
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23
STRUCTURES
M.P. /
TYPE REASON
B.P.
ionic lattice high A large amount of energy must be put in to overcome the strong
electrostatic attractions and separate the giant lattice of ions
simple covalent low Van der Waal’s forces holding the simple molecules together are weak
molecules and can be overcome easily with low amounts of energy
macromolecules high Many covalent bonds must be broken to separate atoms
metallic lattice high A large amount of energy must be put in to overcome the strong
electrostatic attractions between the lattice of cations and the
delocalised electrons surrounding them
25
CEDAR COLLEGE BONDING: OTHER
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