Chapter 7
Chemical Bonding
LEARNING OUTCOMES
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Explain the formation of ionic bonds;
Define and give examples of ionic solids;
Explain the formation of covalent bonds;
Define and give examples of simple molecular
solids;
Explain metallic bonding;
Relate the structure of sodium chloride to its
properties;
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Chapter 7
Chemical Bonding
LEARNING OUTCOMES
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Distinguish between ionic and simple
molecular solids;
Explain the term allotropy;
Define and give examples of giant molecular
solids;
Relate the structure of diamond and graphite
to their properties
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Chemical Bonding
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Atoms bond with each other to obtain the most
stable configuration. They wants to achieve the
nearest noble gas configuration (the most stable
configuration
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This involves the loss, gain or sharing of valence
electrons
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Chapter 7
Chemical Bonding
The Electronic Structure
of Noble Gases
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The noble gases like helium, neon and argon, which are in
Group 0 of the Periodic Table, are very unreactive.
They do not form bonds with other atoms.
They have fully filled outermost (valence) shells.
Except for helium, which has 2 outer electrons, all the other
noble gases have 8 outer electrons.
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Chapter 7
Chemical Bonding
The Electronic Structure
of Noble Gases
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The outer shell of 8 electrons is called an octet
structure and it makes the atom very stable.
E.g. Helium, neon, argon
Atoms of other elements become stable like the
noble gases by losing or gaining electrons or by
sharing electrons.
They achieve this by forming bonds with other
atoms.
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Chapter 7
Chemical Bonding
Types of Bonds
Metallic
Bonding
Covalent Bond
Ionic Bond
Sharing of Electrons
Sea of Electrons
Transfer of Electrons
Positive cations + electrons
Between Non-metals
Between Metal + Non-metal
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Chemical Formulae and Compounds
Ionic and Covalent bonding results in the formation of
chemical compounds:
● Chemical formulae can be used to represent chemical
compounds
○ Chemical formula shows which elements are present in a
compound and shows the ratio between the elements.
○ Chemical formulae can be written in three ways:
■ Molecular formula: gives the actual number of atoms of each
element present in one molecule of a compound,
● e.g. the molecular formula of ethene is C2H4
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Structural formulae: gives the diagrammatic
representation of one molecule of the compound. Lines
between the atoms are used to represent bonds
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Chemical Formulae and Compounds
Empirical Formula:this gives the simplest whole
number ratio between the elements in the compounds.
■ e.g. the empirical formula of ethene is CH2
Writing empirical formula (see pg 66 to 68 of Csec for
chemistry)
https://youtu.be/VnzIqpdEims Formula for ionic compounds
https://youtu.be/KrJnnwLDY6o Formula for covalent compounds
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Chapter 7
Chemical Bonding
Ionic Bonding:
https://youtu.be/zpaHPXVR8WU
https://youtu.be/6DtrrWA5nkE
Ionic Bonds
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When sodium reacts with chlorine, the sodium atom loses
an electron to become a positively charged sodium ion:
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Chapter 7
Chemical Bonding
Ionic Bonds
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The chlorine atom gains an electron to become a
negatively charged chloride ion:
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Chapter 7
Chemical Bonding
Ionic Bonds
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The positive sodium ion and the negative chloride ion then
attract each other to form sodium chloride.
■ Sodium chloride is called an ionic compound.
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Chapter 7
Chemical Bonding
Other ionic compounds
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Another example of an ionic
compound is that formed
between magnesium and
chlorine.
Each magnesium atom
transfers 2 electrons, one to
each chlorine atom, to form
magnesium chloride.
The formula of magnesium chloride is therefore
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given as MgCl2.
Chapter 7
Chemical Bonding
Quick check 1
1. Ionic bonds are formed between a ______ and a _____.
2. A metal atom ______ an electron to form a _______ ion while
a non-metal ______ an electron to become a ________ ion.
3. The two oppositely charged ions ________ each other to form
an ______ compound.
4. An ionic bond is formed by the _________ of _______.
5. (a) Is aluminium oxide an ionic or covalent compound?
(b) State the formula of aluminium oxide.
Solution
13
Chapter 7
Chemical Bonding
Solution to Quick check 1
1. Ionic bonds are formed between a metal and a non-metal.
2. A metal atom loses an electron to form a positive ion while
a non-metal gains an electron to become a negative ion.
3. The two oppositely charged ions attract each other to form
an ionic compound.
4. Ionic bond is formed by the transfer of electrons.
5. (a) Aluminium oxide is an ionic compound.
(b) Al2O3
Return
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Chapter 7
Chemical Bonding
https://youtu.be/5I_1jRGSR9E covalent compound
Covalent Bonds
■ A hydrogen atom has only one electron in its first shell.
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To achieve a more stable structure like helium, it needs one
more electron in the first shell.
So two hydrogen atoms join together and share their
electrons. A hydrogen molecule is formed.
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Chapter 7
Chemical Bonding
Covalent Bonds
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This sharing of electrons is called covalent bonding.
In an oxygen atom, the outer shell has 6 electrons, so to achieve
an octet structure of 8 electrons like neon, two oxygen atoms
combine to share 4 electrons.
This is called a double bond.
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Chapter 7
Chemical Bonding
Other covalent molecules
Methane
H
Water
H
C
H
H
O
H
H
CH4 (4 single bonds)
H2O (2 single bonds)
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Chapter 7
Chemical Bonding
Quick Check 2
1. The joining of atoms to form a molecule is called
__________ ________ .
2. The two types of bonds are ________ bond and
________ bond.
3. Covalent bonds are formed by the _________ of
_________ .
4. Ionic bonds are formed by the __________ of_________ .
5. _________ ______ are formed between non-metals
e.g. hydrogen, oxygen and carbon.
Solution
18
Chapter 7
Chemical Bonding
Lesson 2
Solution to Quick check 2
1. The joining of atoms to form a molecule is called
chemical bonding .
2. The two types of bonds are covalent bond and
ionic bond.
3. Covalent bonds are formed by the sharing of
electrons .
4. Ionic bonds are formed by the transfer of
electrons .
5. Covalent bonds are formed between non- metals e.g. hydrogen,
oxygen and carbon.
Return
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Chapter 7
Chemical Bonding
Properties of Covalent Compounds
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The intermolecular forces
between the molecules are
weak so covalent
compounds have low melting
and boiling points.
For example, water, a
covalent compound, has a
melting point of 0 oC and a
boiling point of 100 oC.
Weak intermolecular
forces
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Chapter 7
Chemical Bonding
Properties of Covalent Compounds
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Covalent compounds do not
conduct electricity in any
state.
Most covalent compounds
are insoluble in water.
Instead they are soluble in
organic solvents.
For e.g. iodine is insoluble in
water, but soluble in ethanol.
water
Pure water does not
conduct electricity
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Chapter 7
Chemical Bonding
Properties of Ionic Compounds
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The electrostatic forces
between the
oppositely-charged ions are
very strong so ionic
compounds have very high
melting points and boiling
points.
For e.g. sodium chloride, an
ionic compound, has a
melting point of 801 oC and
a boiling point of 1 517oC.
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Chapter 7
Chemical Bonding
Properties of Ionic Compounds
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Ionic compounds conduct
electricity when molten or
dissolved in water. This is
because the ions can move about
and conduct electricity.
■ Most ionic compounds are soluble in
water, but insoluble in organic solvents.
For e.g. sodium chloride is soluble in
water, but insoluble in oil or petrol.
Molten sodium
chloride conducts
electricity.
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Chapter 7
Chemical Bonding
Summary
Differences between Ionic and Covalent Compounds
Ionic Compounds
Covalent Compounds
Have very high melting and boiling
points
Have low melting and boiling points
Conduct electricity when molten or in
aqueous solution
Cannot conduct electricity in any state
Are usually soluble in water, but
insoluble in organic solvents
Are usually insoluble in water, but
soluble in organic solvents
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Chapter 7
Chemical Bonding
Quick check 3
1. Covalent compounds have _______ forces of attraction
between the molecules, so they have ____ melting points and
______ boiling points.
2. Ionic compounds have very ______ forces of attraction
between the oppositely charged ions, so they have very
______ melting points and ______ boiling points.
3. All covalent compounds cannot _____ _______ .
4. All ionic compounds can conduct ________ when they are
_______ or ________ in water.
5. Sugar is a covalent compound but it is soluble in water. State
one test you would use to show that sugar is a covalent
compound.
Contd.
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Chapter 7
Chemical Bonding
Quick check 3 (cont.)
6. The table below shows 3 substances.
Substance
Electrical Conductivity
when solid
when molten
A
does not conduct
does not conduct
B
does not conduct
conducts
C
conducts
conducts
(a) Which substance is an ionic compound?
(b) Which substance is a metal?
(c) Which substance could be a covalent compound?
Solution
26
Chapter 7
Chemical Bonding
To learn more about Chemical Bonding,
click on the links below!
1.
http://www.quia.com/jq/19617.html
2.
http://www.purchon.com/chemistry/bonding.htm
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Chapter 7
Chemical Bonding
Solution to Quick check 3
1. Covalent compounds have weak forces of attraction between the
molecules, so they have low melting points and low boiling
points.
2. Ionic compounds have very strong forces of attraction between
the oppositely charged ions, so they have very high melting
points and high boiling points.
3. All covalent compounds cannot conduct electricity.
4. All ionic compounds can conduct electricity when they are molten
or dissolved in water.
5. Dissolve some sugar in water, then try to pass electricity through
it. The sugar solution will not able to conduct electricity.
Contd.
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Chapter 7
Chemical Bonding
Solution to Quick check 3 (contd.)
6. The table below shows 3 substances.
Substance
Electrical Conductivity
when solid
when molten
A
does not conduct
does not conduct
B
does not conduct
conducts
C
conducts
conducts
(a) Ionic compound: B
(b) Metal: C
(c) Covalent compound: A
Return
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Chapter 7
Macromolecular Structures
Simple molecules
■ Many covalent substances like water,
methane, carbon dioxide and iodine
exist as small molecules.
■ These compounds are said to have
simple molecular structures.
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Chapter 7
Macromolecular Structures
Macromolecules
■ Some covalent substances like silicon
dioxide (SiO2), diamond and graphite
are made up of very large molecules.
■ These substances are said to have
macromolecular structures.
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Chapter 7
Macromolecular Structures
Properties of Macromolecules
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Due to the large structures of these macromolecules,
their chemical and physical properties are different
from those of the simple molecules.
The macromolecules are solids with very high melting
and boiling points.
E.g. The melting point of diamond is 3550 oC,
compared to 0 oC for water.
Due to their sizes, they are also not as reactive
compared to the simple molecules.
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Chapter 7
Macromolecular Structures
Metallic bonding
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Metals are also made up of very large lattice structures.
The metallic structure consists of a lattice of positive ions
in a “sea of electrons”.
Metals are malleable because the layers of atoms can
slide over one another easily as they are being arranged
in neat layers.
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Chapter 7
Macromolecular Structures
Properties of Metallic structure
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The closely packed positively charged metallic ions
form a lattice structure with the outer electrons
moving freely around the whole metallic structure.
The electrostatic attraction between the metallic
ions and the electrons holds the metallic ions tightly
in the lattice and this gives the metal a high
melting point.
The free electrons are able to move and
conduct electricity and heat.
This explains why metals are good
conductors of heat and electricity.
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Chapter 7
Macromolecular Structures
Van der Waals Forces
-Van der Waals forces of attraction can exist
between atoms and molecules.
-They are not the same as ionic or covalent
bonds. They arise because of fluctuating
polarities of nearby particles.
-The shape and size of molecules affect the
strength of the van der Waals forces. The
larger the force, the higher the melting and
boiling point.
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Chapter 7
Macromolecular Structures
Structure of diamond
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In diamond, each carbon atom is linked to four other
carbon atoms by strong covalent bonds.
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The carbon atoms are arranged in a tetrahedral
structure which extends throughout the whole diamond
lattice made up of millions of atoms.
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Structure of
diamond
The diamond structure is very rigid and the bonds are
very strong and difficult to break. This explains why
diamond is very hard and strong and has a very high
melting point (3550 ºC) and very high boiling point
(4827 ºC).
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Chapter 7
Macromolecular Structures
Structure of graphite
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In graphite, each carbon atom is linked to three other
carbon atoms in the same plane by strong covalent
bonds.
The
carbon atoms form six-member hexagonal rings that link up
to form flat layers.
The hexagonal rings are arranged in parallel layers with weak
forces of attraction between the atoms in each layer.
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Chapter 7
Macromolecular Structures
Properties of graphite
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strong covalent
bonds
The covalent bonds between the atoms in each
layer are strong, and a lot of heat energy is
required to break these bonds when graphite
melts. This explains why graphite has a very
weak forces
high melting point (3652 oC ).
Not all the electrons in graphite are
used in bonding. There are some free
electrons which enable graphite to
conduct electricity.
The forces of attraction between the atoms in each
layer is weak. The layers can easily slide away from
each other when a force is applied. For this reason,
graphite is smooth and slippery.
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Chapter 7
Macromolecular Structures
Summary of properties
Property
Diamond
Graphite
Hardness and
Texture
Very hard and strong Soft, smooth and
slippery
Melting point and
Boiling point
Very high
Very high
Electrical
Conductivity
Does not conduct
electricity
Conducts electricity
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Chapter 7
Macromolecular Structures
Uses of diamond
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Due to their differences in properties, diamond and
graphite are used in different ways.
Diamond being hard and strong, is used for making
cutting and drilling tools.
Another use for diamond is for making jewellery.
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Chapter 7
Macromolecular Structures
Uses of graphite
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Graphite being smooth and slippery, is used in making
lubricants for use in machinery, motorcar engines and
even bicycle chains.
Graphite being chemically unreactive and a conductor
of electricity, is used in making electrodes for use in
electrolysis and in dry cells.
Due to its very high melting point, graphite is used as
a heat insulator. It is used to coat the nose of a
space shuttle.
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Chapter 6
Macromolecular Structures
Quick check 4
1.The table below shows the properties of 4 substances.
Element
Conducts electricity in
Melting point
(OC)
Solid state
Liquid state
W
good
good
1085
X
poor
good
801
Y
poor
poor
3550
Z
poor
poor
114
Deduce the type of bonds that each substance has.
Solution
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Chapter 6
Macromolecular Structures
Quick check 4 (cont’d)
2.The pictures below show 4 types of molecular structures.
A
C
B
D
Identify the substance or the type of bonds shown
by each structure.
Solution
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Chapter 7
Macromolecular Structures
Solution to Quick check 4
1.
2.
W: metallic bonding, X: ionic bonding,
Y: macromolecular (diamond), Z: simple molecular
A: graphite; macromolecular
B: silicon dioxide; macromolecular
C: metallic bonding
D: ionic crystal lattice
Return
44
Chapter 7
Macromolecular Structures
To learn more about Macromolecular Structures,
click on the links below!
• http://mineral.galleries.com/minerals/elements/graphite/graphite.htm
• http://www.chemguide.co.uk/atoms/bonding/metallic.html
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