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Why do atoms bond?
They want to have a full outer electron shell.
This is why oxygen that we breathe in is O2, chlorine gas is
Cl2 etc…
What type of bond?
METAL
NON-METAL
METAL
NON-METAL
metallic
ionic
ionic
covalent
What are the properties of the different
types of chemical bond?
IONIC
Type of
structure
Are ions
present?
Are delocalised
electrons
present?
How strong is
the chemical
bond?
High/Low
melting point?
Conductor of
electricity?
METALLIC
COVALENT
COVALENT
What are the properties of the different
types of chemical bond?
IONIC
METALLIC
COVALENT
COVALENT
Type of
structure
giant
giant
Giant
Simple
molecules
Are ions
present?
yes
yes
no
no
Are delocalised
electrons
present?
no
yes
no (except
no
very
strong
in graphite)
How strong is
the chemical
bond?
strong
strong
very
strong
High/Low
melting point?
high
high
low
very high
Conductor of
electricity?
when molten/
in solution
yes
no (except
no
graphite)
What is an ionic bond?
Li
Li
What’s missing?
Giant Ionic Structures
Oppositely charged ions are
attracted to each other.
This attraction forms a strong
ionic bond.
The charge on a ion acts in
all directions.
The ions arrange themselves
into a lattice structure,
involving huge numbers of
ions, which is why they are
named giant structures.
When an ionic
substance
dissolves, the
ions break out of
their lattice
structure and are
free to move
about and carry
a charge.
Because of this, an electric current can be passed
through the solution.
The same is true when ionic substances are molten.
When atoms share electrons, they are
held together very tightly. This is a
covalent bond.
Example – Hydrogen:
x
H
H
Hydrogen atoms
H
x H
Hydrogen molecule
H2
H
H
C
H
H
You are very likely to get a question about why giant
covalent substances (like diamond or silicon dioxide –
sand) have very high melting points.
Lots (thousands,
millions!) of atoms
joined together by
covalent bonds
• very strong bonds
• lots of bonds to be broken
• need a huge amount of
energy/heat to break the bonds
• therefore a very high melting
point
Simple covalent substances
(molecules)
Molecules: a small number of atoms covalently
bonded.
They have very different properties to giant
covalent substances.
Simple molecules all have low melting and
boiling points.
Why?
The covalent bonds are very
strong, so the atoms are held
together tightly.
H H
H
x
H
But, the individual molecules
are separate from each
other.
There is a force of attraction between individual molecules
(called the intermolecular force). This is weak, and only
a small amount of energy is needed to overcome it.
Cl
Cl
STRONG
covalent bond
WEAK
intermolecular
force
When a molecular substance
melts/boils, it is the intermolecular
forces that are overcome.
The covalent bonds are not broken.
Finally, metallic bonds
• outer shell electrons delocalise (come away from the atom) and are
free to move
• forming a ‘sea of electrons’ and leaving positive metal ions
• the attraction between negative electrons and the positive ions
holds the metal together – the electrons act like glue
• the metal ions are held tightly in neat rows that can slide over each
other

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