C2 Revision

C2 Revision

Isotopes
1. atoms of the same element with different masses
Relative Formula Mass
1. atomic mass of each element x number of atoms present in formula and add up e.g. (40x1) + (32x1) + (16x4) = 136
Ionic Bonding
1. Metal reacting with non-metal
  1. metal atoms lose electrons and become positive ions
  2. non-metal atoms gain electrons and become negative ions
  3. Oppositely charged ions are electrostatically attracted
Ionic Lattices
1. oppositely charged ions attract each other in all directions
2. melting and boiling points are high because it is hard to separate the electrons from one another
Covalent Bonding
1. atoms of two non-metals combining
2. outer electron shells overlap, sharing
3. nuclei of both atoms in a cov. bond are positively charged
4. cannot conduct electricity because they have no charged particles to move around
  1. cannot dissolve in water
    1. weak intermolecular forces - easily broken, providing low bp and mp
Covalent Lattices
1. giant structures
2. diamond - each carbon atom joined to four other carbon atoms, hardest natural substance, cannot conduct electricity
  1. tetrahedral structure
3. graphite - each carbon atom in layer is joined to three other carbon atoms, layers slide over one another because there are no covalent bonds, soft=lubricant and pencils, conducts electricity
4. silicon dioxide - similar to diamond structure
Thermosoftening
1. soften when heated and can be shaped when hot. shape will harden when it is cooled, but can be reshaped when heated up again. poly(ethene) is a thermosoftening polymer. tangled polymer chains can uncoil and slide past each other, making it a flexible material.
2. Thermosetting
  1. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.
Alloys
1. in pure metal, all atoms are the same size and therefore are very soft because atoms can slide
  1. alloys disrupt the regular lattice, preventing layers from sliding due to the myriad of different sized atoms
Gas Chromatography
1. separating technique
2. send gas solvent with analysed substances down a tube filled with solid material. components travel at dif speeds and are detected at the end.
OXIDATION IS LOSS, REDUCTION IS GAIN
Empirical Formula
1. 1. work out the relative formula mass
  1. 2. find mass of element in compound
    1. 3. divide by rel.form. mass x100 to get percentage
Percentage Yield
1. percentage obtained/maximum theoretical mass x100
Collision Theory
1. reactants must collide to form chemical reaction. increasing the temperature provides particles with more energy, so they vibrate more and heat up more, causing more collisions to happen.
  1. to cause reaction, particles must collide with sufficient energy to break bonds - this minimum energy is called activation energy
Catalysts
1. chemicals that speed up relations but are not used up in the process
2. lowers the activation energy, so that more collisions happen at a faster rate, without having to build up to a higher minimum energy
Endothermic and Exothermic
1. Endothermic
  1. heat enters the reaction - cools
    1. electrolysis
    2. thermal decomposition in a blast furnace
2. Exothermic
  1. heat exits - warms surroundings through heat transfer
    1. burning
    2. neutralisation between acids and alkalis

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