C2

• Pure substance


  A single element or compound, not mixed with any other substance
• Pure substance (everyday language)


  Substance that has had nothing added to it, so it is unadulterated and in its natural state
• Pure substances


  Melt and boil at specific temperatures
• Impure substances


  Melt and boil over a range of temperatures
• Relative formula mass


  Sum of the relative atomic masses of the atoms in the numbers shown in the formula
• Relative formula mass (in a balanced chemical equation)

  Sum of Mr of reactants in quantities shown = sum of Mr of products in quantities shown
• Relative atomic mass


  Ratio of the average mass of one atom of an element to 1/12th of the mass of an atom of carbon-12
• Relative molecular mass


  Ratio of the average mass of one molecule of an element or compound to 1/12th of the mass of an atom of carbon-12
• Relative formula mass


  Weighted average of the masses of the formula units relative to 1/12th of the mass of a carbon-12 atom
• Empirical formula


  Simplest whole number ratio of atoms of each element in a molecule
• Molecular formula


  Tells you how many atoms of each element are in a molecule
• Formulation


  Mixture that has been designed as a useful product
• Useful materials that are formulations of mixtures

  • Food and drink products
  • Medicines
  • Sunscreens
  • Perfumes
  • Paints
• Alloy


  Metal mixed with small amounts of similar metals to make it harder for everyday use
• Filtration


  Separate precipitate from salt solution
• Crystallisation


  1. Warm solution to evaporate solvent

  2. Allow solution to cool to grow crystals

  3. Collect and dry crystals
• Simple distillation


  Separate solvent from solution by heating to evaporate solvent, then condense vapour
• Fractional distillation


  Separate mixture of liquids with different boiling points by heating and condensing at different temperatures in a fractionating column
• Chromatography


  Separation technique involving a stationary phase and a mobile phase, separation depends on distribution between phases
• Paper chromatography


  Stationary phase = paper, mobile phase = solvent
• Thin layer chromatography (TLC)

  Stationary phase = thin layer of inert substance on flat surface, mobile phase = solvent
• Rf value


  Distance moved by substance / distance moved by solvent
• Different compounds have different Rf values in different solvents, which can help identify the compounds
• A pure compound will produce a single spot on a chromatogram, while a mixture will separate into different spots
• Gas chromatography


  Mobile phase = inert carrier gas, stationary phase = liquid/solid on solid support, separation depends on solubility in gas
• Metals


  Elements that react to form positive ions
• Metals


  • Majority of elements are metals
  • Found to the left and towards the bottom of the periodic table
  • They lose electron(s) in order to form positive ions
  • Typically shiny, good electrical conductors, are dense and have high melting points

  
• Non-metals


  Elements that react to form negative ions
• Non-metals


  • Found towards the right and top of the periodic table
  • They gain electron(s) in order to form negative ions
  • Typically dull in appearance, poor electrical conductors, aren't dense and have low melting points

  
• Elements are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups
• Group number


  Refers to the number of outer shell electrons
• Carbon


  Can form four covalent bonds
• Organic compounds


  • Occur due to carbon's ability to form families of similar compounds, chains and rings
• Period number


  Refers to the number of shells of electrons
• Diamond


  Each carbon is joined to 4 other carbons covalently. Very hard, high melting point, does not conduct electricity.
• Ionic bonding


  • Formed between a metal + non-metal: electrons in the outer shell of the metal atom are transferred to the nonmetal
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
• Graphite


  Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings with no covalent bonds between the layers. Layers can slide over each other, making it soft and slippery. One electron from each carbon is delocalised, allowing it to conduct electricity.
• Ionic compound


  • Sodium chloride (salt): Na+ (small blue particles) and Cl- (larger green ones)
• Fullerenes


  Molecules of carbon atoms with hollow shapes, based on hexagonal rings of carbon atoms but may also contain rings with five or seven carbon atoms. The first fullerene discovered was Buckminsterfullerene (C60) which has a spherical shape.
• Ionic compounds


  • Have regular structures (giant ionic lattices) in which there are strong
  • Have high melting and boiling points, because a lot of energy is required to break the many strong bonds
  • When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and carry current