AQA Chemistry Unit 2 (C2)

KEY FACTS on Unit 2 Chemistry 

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  • Created by: Triciaaa
  • Created on: 03-01-13 22:07

C2.1 Structure and Bonding

  • Particles found in atoms: proton, neutron, electron
  • Atomic number (bottom) = no. of protons (same no. of electrons)
  • Mass number (top) = no. of protons and neutrons
  • Compound = substance containing 1+ elements

Ionic bonding
> ion - atom that has gained/lost electrons
> when an ion has a positive charge = lost electrons
> when an ion has a negative charge = gain electrons

Covalent bonding
>sharing electrons
>e.g. hydrogen and oxygen (2 hydrogens and 1 oxygen)  

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C2.2 Structure and Properties

There are 4 key types of structures you need to know:

Giant covalent, Giant ionic, Simple covalent and Metallic structures

  • Giant covalent = e.g. diamond and graphite
    - high melting+boiling pt. 
    - strong covalent bond
    -requires a lot of energy to break bonds away
    - doesnt conduct electricity
  • Giant ionic = e.g. sodium chloride
    - high melting+boiling pt.
    - strong electrostatic forces of attraction
    - conducts electricity 
  • Simple covalent = e.g. carbon dioxide
    - low melting+boiling pt.
    - strong covalent bond
    - weak intermolecular forces
    - usually gas at room temp
  • Metallic structure
    - giant structure
    - delocalised electrons
    - conduct electricity
    - strong electrostatic forces of attraction 


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C2.3 Quantitative Chemistry


Relative Atomic Mass (Ar) - top no. of the element e.g. Lithium Ar = 7

Relative Formula Mass (Mr) - total no. of atomic masses in a compound e.g. CO2 = 12+(2x16=32) Mr = 44

Percentage mass - Ar/Mr x 100 

Moles - mass/mr 

Percentage yield - actual/predicted x 100

Mass in reactions - balance equation, work out Mr, divide to get 1, multiply to get what you want

Empirical formula - list all elements, write down experiment masses, divide by Ar, nice ratio 


Paper - the higher the chemical moves up paper, the more its dissolved by solvent

Machines - Advantages = fast, accurate, sensitive

Gas - separates gases in column, measures retention time and how many gases 

Mass spectrometry - measuring relative molecular mass

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C2.4 Rates of Reaction

more kinetic energy, vibrate more, move quicker, more frequent collisions

Concentration (+pressure)
more particles to collide with, more frequent collisons
in a gas - more squashed up  

Surface Area
more area to collide on, more frequent collisons 

speeds up reaction without being CHANGED or USED UP in a reaction
- reduce costs = never used up, less fuel costs, requires low temperature
-BUT can be POISONED by impurities, only specific to one reaction

activation energy - least amount of energy required to start up the reaction  

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C2.5 Exothermic and Endothermic Reactions

Exothermic - release/give off heat to surroundings e.g. oxidation or neutralisation reactions
- hand warmers, self heating cans

Endothermic - takes in heat from surroundings, fall in temperature e.g. thermal decomposition reactions
- sport injury packs

Reversible reactions - 
>>>> = exothermic
<<<< = endothermic 

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C2.6 Acids, Bases and Salts


acid + base = salt + water
acid + metal = salt + hydrogen
acid + metal hydroxide = salt + water
acid + metal oxide = salt + water


Soluble salts - alkali, metal or insoluble base 
Insoluble salts - precipitation 

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C2.7 Electrolysis


Electrolysis - process whereby an electric current passes through an electrolyte and is decomposed by it 

Electrolyte - an ionic substance (either molten or dissolved in solution) where an electric current is passed through

Anode - positive electrode

Cathode - negative electrode

Oxidation - gain of electrons (OIL)

Reduction - loss of electrons (RIG)

Electroplating - using electrolysis to coat a metal with another metal 

Examples that need to be learnt

Aluminium oxide - cryolite, carbon dioxide is produced at anode

Brine (NaCl) - useful products = sodium hydroxide, chlorine, hydrogen 

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