Chemistry
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| Covalent bonding | When non-metals share electrons in order to gain a full outer shell. They must share the same amount as they want to gain
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| Covalent bonding is shown by | Dot and cross diagrams
- With one - representing a pair of shared electrons
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| Ionic bonding | The formation of ions through the loss or gain of electrons
Happens between metals and non-metals with the strong opposite attraction charge holding the bond together
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| Metallic bonding | Atoms lose their outer electron resulting in lots of positive charged atoms surrounded by a sea of delocalised electrons to prevent them from rebelling.
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| Properties of metallic bonding | Good conductors due to sea of delocalised electrons
Tough as lattice layers can easily slide over one another
Malleable and ductile as lattice layers can move
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| Diamond | A giant covalent structure.
4 bonds to each carbon resulting in a high m.p and b.p
Insoluble in water
Not conductible as no free electrons
Very strong as formed under lots of pressure and high temperatures
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| Graphene | 3 strong covalent bonds around each carbon so one delocalised electron.
Hexagonal layers held together by delocalised electrons
Weak inter-layer forces
High m.p and b.p
Layers can slide over each other so a lubricant
Conducts due to electron
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| Silica | Three oxygen bonded to a silicon atom with no free electrons
High melting and boiling point
Hard
Heat resistant so used as a fire retardant
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| Giant Ionic structures | Positive ions are surrounded by negative ions and vice versa
Strong attraction between + and - so high m.p and b.p
Soluble in water
Does not conduct when a solid, only when molten or a liquid
Brittle as like charges would be pushed together repelling
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| Simple molecular structures | Strong covalent bonds between atoms but weak intermolecular forces
Often liquid and gases
No free electrons so don't conduct
Do not dissolve in water
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| Alloys | Metals mixed with another element to disrupt pattern and so make it stronger
High-carbon steel is hard but brittle, a good conductor
Low-carbon steel is ductile, corrosive and a good conductor
Chromium steel is tough and corrosive resistant
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| Nano science | 1-100 nm small
Antimicrobial- Nano silver so used for medical stuff
Absorbs UV rays but stays transparent- Nano zinc oxide
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| Bucky balls | Buckminster fullerene are very strong due to it's covalent bonds
Unreactive and can penetrate cell walls
Used for drug administration
Environmental and health implications
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| Graphene | A single layer of graphite so very strong, flexible and a good conductor
Used for electronics and bulletproof vests
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| Fullerene | A nanotube made out of graphene
High length to diameter ratio so very strong
Used for bike frames
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| Properties to uses of Nano-technology (4) | -High conductivity-> micro electronics
-Strength -> Building materials enhancing
- High tensile strength-> Wires
- Light-> Overhead cables, sports equipment
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| Pros and Cons of nanotechnology | P- New properties so world of opportunity
N- Hard to track so unknown health and environmental impacts
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| Shape memory polymers | Remember shape when heated.
Uses- repairing wires
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| Shape memory alloys | Remember shape when heated but a metal
Uses- Orthodontic braces, stents, glasses frames
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| Thermochromic dyes | Changes colour wit heat
Uses- Thermometer, colour changing mugs
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| Photochromic dyes | Changes colour with light
Uses- T-shirts and glasses to sunglasses
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| Polymorph | Low melting point to be easily moulded
Uses- Gumshields
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| Hydrogels | Can shrink and swell by holding lots of water in it's polymer chains. Also responds to temperature and pH
Uses- nappies, absorbing toxic spillages
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