atomic structure and periodic table

• Element


  A substance in which all the atoms are the same
• Compound


  A substance containing two or more different elements chemically combined in fixed proportions
• Compounds have different properties from the elements they are made of
• To separate a compound back into its elements, a chemical reaction is required
• Mixture


  A combination of different elements or compounds that are not chemically combined
• Mixtures can be separated using physical separation techniques like filtration, distillation, crystallization or chromatography
• Molecule


  A group of atoms chemically combined, even if they are the same element
• Molecules


  • Methane
  • Water
  • Ammonia
• Molecules containing the same element are not compounds
• Molecules containing the same element

  • Chlorine molecule
  • Oxygen molecule
• Physical separation techniques can only be used to separate mixtures, they cannot be used to separate the elements in a compound
• Chemical reactions such as reduction or electrolysis can be used to separate the elements in compounds
• Filtration


  Used to separate an insoluble solid from a liquid
• Insoluble


  The solid will not dissolve in the liquid
• Example of insoluble solid and liquid


  • Silver chloride (s) and water (l)
• Filtration process


  1. Pour mixture into filter paper

  2. Liquid (filtrate) passes through

  3. Solid trapped in filter paper
• Crystallization


  Used to separate a soluble solid from a liquid
• Example of soluble solid and liquid


  • Sodium chloride (aq) and water (l)
• Crystallization process


  1. Leave solution to evaporate

  2. Water evaporates

  3. Solid sodium chloride crystals left behind
• Heating can be used to speed up crystallization, but some chemicals may break down when heated
• Simple distillation


  A physical separation technique used to separate a dissolved solid from a liquid, where the liquid is kept
• Simple distillation


  1. Evaporate the liquid by heating

  2. Condense the vapor back to a liquid by cooling
• Apparatus for simple distillation

  • Flask with solution
  • Continuous glass tube
  • Condenser with cold water circulation
  • Thermometer
• Heating the solution


  Liquid starts to evaporate, turning into a vapor
• Vapor passing through the condenser


  Vapor condenses, turning back to a liquid
• Simple distillation can be used to produce drinking water from seawater
• Simple distillation requires a great deal of energy, so it is generally not used to produce drinking water
• There is another type of distillation called fractional distillation, which will be covered in the next video
• Fractional distillation


  A method to separate a mixture of different liquids based on their different boiling points
• Fractional distillation apparatus


  • Flask containing liquid mixture
  • Fractionating column with glass beads
  • Thermometer at top of column
  • Condenser
• Fractional distillation process


  1. Heat mixture to evaporate liquids

  2. Vapors enter fractionating column

  3. Vapors condense and drip back into flask

  4. Repeated evaporation and condensation separates liquids by boiling point

  5. Thermometer monitors temperature to identify when pure fractions are collected
• Liquids must have different boiling points for fractional distillation to work
• If liquids have very similar boiling points, it's harder to separate them and multiple rounds of fractional distillation may be needed
• Fractional distillation is not suitable for separating very large volumes of liquid, like in crude oil refining
• Paper chromatography is a separation technique used by scientists
• Paper chromatography


  • It is a physical process, not a chemical reaction
  • It separates substances based on their different solubilities
• Substances that can be separated by paper chromatography

  • Colored inks from pens
• Paper chromatography procedure


  1. Draw a pencil line at the bottom of chromatography paper

  2. Put dots of different colored inks on the line

  3. Place the bottom of the paper in a solvent

  4. Solvent moves up the paper, dissolving and carrying the ink

  5. Substances separate based on their solubility
• Stationary phase


  The paper, which does not move
• Mobile phase


  The solvent, which moves up the paper