Chemistry 2A
- Created by: annabertram
- Created on: 10-02-15 15:40
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- Chemistry 2A
- Isotopes
- "Different atomic forms of the same element, which have the same number of protons but a different number of neutrons."
- They have the same atomic number but different mass numbers.
- Ionic Bonding
- Atoms lose or gain electrons to form charged particles (ions).
- Ionic compounds have giant ionic lattices.
- There are very strong electrostatic forces of attraction between oppositely charged ions, in all directions.
- Ionic compounds have high melting and boiling points due to the strong attraction.
- When they melt, the ions are free to move and can carry electric current.
- They also dissolve easily in water. The ions separate, are then free to move and carry electric current.
- When they melt, the ions are free to move and can carry electric current.
- It is between a metal and a non-metal.
- Group 1 and 2 elements are metals, they lose electrons and form positive ions.
- Group 6 and 7 elements are non-metals, they gain electrons and become negative ions.
- Covalent Bonding
- Atoms share electrons so that they've got full outer shells,
- Having a full outer shell gives them the electronic structure of a noble gas.
- Substances with covalent bonds can either be simple molecules or giant structures.
- Simple Molecules.
- The atoms form very strong covalent bonds to form small molecules.
- The forces of attraction between the molecules are very weak.
- Because of these weak intermolecular forces, the melting and boiling points are very low.
- They don't conduct electricity because there are no ions so there is no electrical charge.
- Giant Structures.
- All of the atoms are bonded to each other by strong covalent bonds.
- They have very high melting and boiling points.
- They don't conduct electricity (except for graphite).
- The main examples are diamond and graphite.
- All of the atoms are bonded to each other by strong covalent bonds.
- Simple Molecules.
- Atoms share electrons so that they've got full outer shells,
- Metallic Structures
- Metals consist of a giant structure.
- Metallic bonds involve delocalised ('free') electrons.
- This makes metals good conductors of heat and electricity.
- They allow the layers of atoms to slide over each other, allowing metals to be bent and shaped.
- There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
- Alloys
- The atoms are different sizes which distorts the layers, making it harder for them to slide over each other.
- Alloys are harder than pure metals.
- The atoms are different sizes which distorts the layers, making it harder for them to slide over each other.
- New Materials
- Smart materials behave differently depending on the conditions, e.g. temperature.
- An example of a smart material is Nitinol. It is used for glasses frames and dental braces as it is a "shape memory alloy."
- Nanoparticles are minute and contain a few hundred atoms.
- Many new uses of nanoparticles are being developed.
- They have a huge surface area to volume ratio so they could help make catalysts.
- Nanotubes conduct electricity so can be used in tiny electric circuits.
- Many new uses of nanoparticles are being developed.
- Smart materials behave differently depending on the conditions, e.g. temperature.
- Polymers
- Forces between molecules determine the properties of the plastic.
- Thermosoftening polymers have individual tangled chains of polymers which are held together by weak intermolecular forces. This means it's easy to melt so you can remould it.
- Thermosetting polymers have stronger intermolecular forces between the polymer chains called crosslinks. These polymers are strong, hard and rigid.
- Low density and high density polythene can be made using different conditions.
- LD polythene = heat ethane to 200°C under high pressure. It's flexible so is used for bags and bottles.
- HD polythene = made at a lower temperature and pressure with a catalyst. It's more rigid so is used for water tanks and drainpipes.
- Forces between molecules determine the properties of the plastic.
- Chromatography
- Paper Chromatography
- Use pencil to draw the baseline.
- Put the filter paper in a beaker with the solvent but keep the solvent below the baseline.
- Gas Chromatography
- The time the substances take to reach the detector is called the retention time.
- The recorder shows a gas chromatograph - the number of peaks shows the number of different compounds.
- It can be linked to a mass spectrometer which identifies substances leaving the column.
- Advantages of using machines = very sensitive, very fast and very accurate.
- Paper Chromatography
- Isotopes
- Metals consist of a giant structure.
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