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Chemistry Unit 2.2 - How structure influences the properties and uses of substances
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Mind Map on Chemistry Unit 2.2 - How structure influences the properties and uses of substances, created by pondcott on 12/31/2013.
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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)
Most compounds between non-metals are molecular
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
Simple Molecular Substances do not conduct electricity
They do not have any free electrons and the molecules do not have electric charges.
Ionic Compounds
Have regular structures (GIANT IONIC LATTICES)
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
When melted or dissolved in water they can conduct electricity
The ions are free to move and carry the current
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
Diamond
Made of carbon atoms, which are joined to FOUR other atoms by strong covalent bonds
Therefore, it is VERY strong and hard
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
One electron is delocalised
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
Metals
Metals conduct heat and electricity
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
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
Shape memory alloys can return to their original shape after being deformed
E.g. Nitinol used in dental braces
Polymers
Very large molecules made from many smaller molecules (monomers)
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
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
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
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
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