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Chemistry Unit 2.2 - How structure
influences the properties and uses
of substances
- Molecules
- Most non-metal elements are molecular
- Most consist of molecules
with just 2 atoms joined
together
- E.g. Oxygen (O2),
Nitrogen (N2)
- E.g. Oxygen (O2),
Nitrogen (N2)
- Most consist of molecules
with just 2 atoms joined
together
- Most
compounds
between
non-metals are
molecular
- E.g. water (H2O),
Carbon Dioxide
(CO2)
- E.g. water (H2O),
Carbon Dioxide
(CO2)
- Intermolecular Forces
- All of these substances have very
strong covalent bonds, but much weaker
forces holding the molecules together
- When one of these substances melts
or boils, it is the weak 'intermolecular
forces' that break, not the strong
covalent bonds
- When one of these substances melts
or boils, it is the weak 'intermolecular
forces' that break, not the strong
covalent bonds
- All of these substances have very
strong covalent bonds, but much weaker
forces holding the molecules together
- Simple Molecular Substances do not conduct
electricity
- They do not have any free
electrons and the molecules do not
have electric charges.
- They do not have any free
electrons and the molecules do not
have electric charges.
- Most non-metal elements are molecular
- Ionic Compounds
- Have regular structures (GIANT IONIC LATTICES)
- In these there are STRONG
ELECTROSTATIC FORCES in
ALL directions between oppositely
charged ions
- In these there are STRONG
ELECTROSTATIC FORCES in
ALL directions between oppositely
charged ions
- Have high melting points
and high boiling points
- Due to the large amounts of
energy needed to break the
strong bonds
- Due to the large amounts of
energy needed to break the
strong bonds
- When melted or dissolved in
water they can conduct
electricity
- The ions are free to move and carry the current
- The ions are free to move and carry the current
- Have regular structures (GIANT IONIC LATTICES)
- Covalent Structures
- Atoms that share electrons can
also form giant structures
- Diamond, Graphite and
Silicon Dioxide are
examples of giant covalent
structures (lattices)
- All of the atoms
in these
structures are
linked to other
atoms by strong
covalent bonds
- Therefore they
have VERY high
melting points
- Therefore they
have VERY high
melting points
- All of the atoms
in these
structures are
linked to other
atoms by strong
covalent bonds
- Diamond, Graphite and
Silicon Dioxide are
examples of giant covalent
structures (lattices)
- Diamond
- Made of carbon
atoms, which are
joined to FOUR
other atoms by
strong covalent
bonds
- Therefore, it is VERY strong and hard
- Therefore, it is VERY strong and hard
- Made of carbon
atoms, which are
joined to FOUR
other atoms by
strong covalent
bonds
- Graphite
- Made of carbon atoms, where
each atom is joined to three
others, forming layers
- The bonds are much weaker than covalent bonds
- This enables the layers to
slide across each other,
making graphite soft
- This enables the layers to
slide across each other,
making graphite soft
- The bonds are much weaker than covalent bonds
- One electron is delocalised
- This allows graphite
to conduct heat and
electricty
- This allows graphite
to conduct heat and
electricty
- Used as pencil lead - As the
pencil moves across the
page, layers of graphite rub
off
- Also used as a lubricant and an electrode in electrolysis
- Also used as a lubricant and an electrode in electrolysis
- Made of carbon atoms, where
each atom is joined to three
others, forming layers
- Atoms that share electrons can
also form giant structures
- Metals
- Metals conduct heat and electricity
- Due to the delocalised electrons in their
structures
- Due to the delocalised electrons in their
structures
- They layers of atoms in metals
are able to slide over each
other
- Therefore, metals can be bent and shaped
- Therefore, metals can be bent and shaped
- Alloys are usually made from 2+ different metals
- Different sized atoms of the
metals distort the layers in the
structure making it more difficult
for them to slide over each other
- This makes alloys harder than pure metals
- This makes alloys harder than pure metals
- Shape memory alloys can return to their original
shape after being deformed
- E.g. Nitinol used in dental braces
- E.g. Nitinol used in dental braces
- Different sized atoms of the
metals distort the layers in the
structure making it more difficult
for them to slide over each other
- Metals conduct heat and electricity
- Polymers
- Very large molecules made
from many smaller molecules
(monomers)
- E.g Ethane -> Polyethene,
Propene -> Polypropene
- E.g Ethane -> Polyethene,
Propene -> Polypropene
- Properties of polymers depend on
what they are made from and the
conditions under which they are made
- Low Density (LD) and High Density
(HD) Polyethene are produced using
different catalysts and reaction
conditions
- Low Density (LD) and High Density
(HD) Polyethene are produced using
different catalysts and reaction
conditions
- Thermosoftening polymers consist of
individual, tangled polymer chains
- Thermosetting polymers consist of
polymer chains with cross-links between
them so that they do not melt when
heated
- Thermosetting polymers consist of
polymer chains with cross-links between
them so that they do not melt when
heated
- Very large molecules made
from many smaller molecules
(monomers)
- Nanoscience
- Refers to structures that are
1-100nm (one billionth of a metre)
- Nanoparticles have a VERY large
surface area compared to their
volume, so they are often able to
react very quickly
- This makes them useful catalysts
- This makes them useful catalysts
- Used in sunscreens to block harmful
ULTRAVIOLET light
- Can lead to the development of...
- New catalysts
- New coatings
- New computers
- Stronger and lighter building materials
- Sensors that detect individual substances in tiny amounts
- Sunscreens and deodorants
- New catalysts
- Refers to structures that are
1-100nm (one billionth of a metre)
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