Transcript Comparing Bonding - Nicks Class Site

KS4 Chemistry
Comparing Bonding
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Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities
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Types of bonding
There are three ways in which atoms can chemically bond.
In each case, electrons are involved in different ways.
 ionic bonding – electrons are transferred from metal to
non-metal atoms to form positive and negative ions. These
oppositely-charged ions are attracted to each other.
 covalent bonding – electrons are shared between
non-metal atoms.
 metallic bonding – electrons become delocalized and
form a sea of free electrons, which attracts positive metal
ions.
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Predicting bonding
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Bonding and structures
The type of bonding in a substance affects the structure of
that substance.
Bonding
Type of
structure
giant ionic
Ionic
lattice
simple
molecular
Covalent
giant covalent
lattice
Metallic
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giant metallic
lattice
Particles in
State at room
structure
temperature
millions of ions solid
few atoms
millions of
atoms
usually liquid or
solid
solid
millions of ions solid (except
mercury – liquid)
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Bonding and properties
The bonding and structure of a substance affects the
properties of that substance.
 Different bonds require different amounts of energy to be
broken – this affects properties such as melting and
boiling point, solubility and hardness.
 Different bonds involve electrons in different ways – this
affects properties such as conductivity of electricity and
heat.
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How do properties differ?
How do the properties of substances differ according to the
type of bonding they contain?
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Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities
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Melting and boiling point: giant structures
Substances with giant structures generally have high
melting and boiling points because all the atoms are strongly
bonded together to form a continuous 3D lattice. A large
amount of energy is needed to break these bonds.
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strong ionic bonds
holds ions together
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strong covalent bonds
holds atoms together
strong metallic
bonds holds ions
together
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Melting and boiling point: molecules
Simple molecular substances have low melting and boiling
points because the forces that hold the molecules together
are weak and easily broken.
strong bonds
within
molecules
weak bonds
between
molecules
In general, the larger the molecule, the higher the melting
and boiling point.
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Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities
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Conductivity – ionic substances
Ionic substances cannot conduct electricity when solid
because the ions are bonded together in the lattice.
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ions cannot move to
carry a charge
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When liquid (molten) or dissolved, however, the ions are able
to break free of the lattice.
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ions are able to move
and carry a charge
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Conductivity – covalent substances
Substances with covalent bonding do not conduct electricity
because all the outer electrons are fixed in shells.
electrons unable
to move and
carry a charge
The exception is graphite, which
has free electrons between layers
of carbon atoms.
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Conductivity – metals
Metals can conduct electricity because the sea of delocalized
electrons between the metal ions are free to move anywhere
in the structure.
sea of electrons
metal
ions
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electrons free to
move and carry an
electrical charge
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Bonding and electrical conductivity
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Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities
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Solubility
Substances with giant covalent or metallic structures
generally do not dissolve easily in water or other solvents.
This is because dissolving involves breaking bonds, which
needs lots of energy.
Many ionic substances dissolve in water because water
molecules have a slight electrical charge and can attract the
ions away from the lattice.
Simple molecular substances are usually insoluble in water
but soluble in solvents such as petrol.
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Strength
Substances with giant structures are generally hard because
a large amount of energy is needed to break ionic, covalent
and metallic bonds.
 Ionic substances are hard but brittle – when a force is
applied, ions with like-charges are brought together.
These repulse each other and cause the lattice to shatter.
 Covalent substances are hard – the covalent bonds do
not bend but break when enough force is applied.
 Graphite is slippery because the weak forces between
layers of carbon atoms can easily be broken.
 Metals are hard but malleable and ductile – the delocalized
electrons allow the metallic bonds to move.
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Density
The density of a substance depends on the type and strength
of bonding and how the atoms/ions are arranged.
Giant substances,
especially metals, are
dense because the
atoms/ions are tightly
packed together.
Substances with simple
molecular structures have lower
densities. The weak forces
between molecules cannot pull
the molecules together tightly.
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strong bonds
cause tight
packing
weak bonds
cause loose
packing
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True or false?
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Effect of structure on properties
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Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities
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Glossary
 covalent bond – A strong bond between two atoms in
which each atom shares one or more electrons with the other.
 delocalized – Electrons that are free to move throughout a
structure. In metals, they form a ‘sea of electrons’.
 ionic bond – The strong electrostatic force of attraction
between oppositely charged ions.
 giant structure – A structure containing millions of atoms
or ions bonded together. The structure extends in three
dimensions until all available atoms or ions are used up.
 lattice – A 3D structure of closely packed atoms or ions.
 metallic bonding – The strong attraction between positive
metal ions and a sea of electrons.
 molecule – A simple structure containing two or more
atoms covalently bonded together.
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Anagrams
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The effect of bonding on properties
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Comparing bonding – team game
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Multiple-choice quiz
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