Chemistry

Chemistry

1. Structure and Bonding

   • Ionic Bonding
     • Between + &- ions
     • Atoms turn into Ions by gaining or losing an electron
     • E.g Mg^2+ 0^2-
     • High melting points
     • Don't conduct electricity when solid
       • Only conduct when molten or in soluion
   • Covalent Bonding
     • Between two non-metals
     • Shared pair of electrons
     • Dot cross diagrams
     • Strong Intermolecular forces
       • Low Boiling point
       • High Melting point
     • The number of covalent binds = 8 - group number
     • Double and triple bonds
       • Double is 2 pairs of shared electrons
       • Triple is 3 pairs of shared electrons
   • Structure properties and uses
     • Simple Molecules
       • Properties
         • Low melting and boiling points
           • Weak intermolecular fores
       • Non-conductive
       • Few atoms joined together
     • Giant Covalent structures
       • Macromolecules E.g
         • Diamond
           • Very hard high melting point each carbon atom is joined to four others.
         • Graphite
           • Is a form of carbon. It forms layers. Each layer is joined by only three other carbon atoms. Graphite is soft used as a lubricant conducts electricity
         • Silica
           • Similar to diamond but silicon and oxygen atoms instead of carbon
     • Polymers
       • LDPE
         • Many branches
         • Weak
         • 85C maximum useable temperature
       • HDPE
         • Few branches
         • Strong
         • 120C maximum useable temp.
       • Thermosoftening polymers
         • No cross links
         • can be reshaped when heated
       • Thermosetting polymers
         • Once heated cannot be reshaped
         • Polymer chains joined with cross links

2. Acids and Bases

   • Acids
     • Uses
       • To remove rust from acids
       • As an electrolyte
     • Found in:
       • Stomach (hydrochloric acid)
       • Lemons (citric acid)
       • Vinegar (acetic acid)
     • All contain hydrogen ions (H+)
   • Bases and alkalis
     • All alkalis are bases but bases aren't always alkali
       • Fried egg diagram
     • All metal oxides and hydroxides are bases
       • Hydroxides are often alkalis
         • NaOH & KOH
   • pH scale
     • Acid Neutral Alkali Red Green Blue
     • Universal Indicator
   • State symbols and spectator ions
     • HCl + NaOH -> H2O +NaCLHCl(aq) +NaOH(nq) -> H2O(l) + NaCl (aq) H+(aq) + Cl-(aq) +Na+(aq) + OH-(aq) -> H20(l) +Na(aq) + Cl (aq)
     • Soluble
       • Most carbonates and hydroxides
       • lead sulphate & barium sulphate
       • lead & silver chlorides bromides & iodides
     • Insoluble
       • sodium potassium & ammonium carbonates and hydroxides
       • all nitrates
       • Most sulphates
       • most chlorides bromides and iodides

3. Energy Changes

   • Exothermic
     • Transfer energy to the surrondings
       • Normally heat energy
         • Causes surroundings to get hotter
     • E.g.
       • Combustion
       • Oxidisation reactions
       • Neutralisation
   • Endothermic
     • Taking energy from the surrondings
     • E.g
       • reaction between ethanoic acid and sodium carbonate
       • Electrolysis
       • Thermal decomposition
   • Reversible reactions
     • A reversible reaction is shown by a Equilibrium symbol
       • ⇌ 

4. Electrolysis

   • Melt
     • + pure sample -expensive -unsafe
   • Dissolve
     • + cheaper + safer - h20 could interfer

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