atomic structure and bonding

• Element


  All of the atoms are the same
• Compound


  Contains two or more different elements chemically combined in fixed proportions
• Compounds usually have totally different properties to the elements that they're made from</b>
• Mixture


  Contains different elements or compounds, but they are not chemically combined
• Separation techniques for mixtures

  • Filtration
  • Distillation
  • Crystallization
  • Chromatography
• Molecule


  Any elements chemically combined, even if they are the same element
• Molecules that are not compounds contain the same element chemically combined
• 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


  A physical separation technique used to separate an insoluble solid from a liquid
• Filtration


  • The liquid passes through the filter paper, the insoluble solid is trapped
• Crystallization


  A physical separation technique used to separate a soluble solid from a liquid
• Crystallization


  1. Dissolve solid in liquid

  2. Allow liquid to evaporate

  3. Solid crystals are left behind
• Heating can be used to speed up the evaporation of the liquid in crystallization, but care must be taken as some chemicals may break down when heated
• State symbols indicate the physical state of a chemical (solid, liquid, gas, dissolved)
• Fractional distillation


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


  • Requires a mixture of liquids with different boiling points
  • Uses a fractionating column containing glass beads to increase the separation of the liquids
• Fractional distillation process


  1. Heat the mixture

  2. Vapors of lower boiling point liquid rise up the fractionating column first

  3. Vapors condense and drip back into the flask

  4. Repeated evaporation and condensation increases the concentration of the lower boiling point liquid

  5. Thermometer measures the temperature, which rises and then plateaus at the boiling point of the lower boiling point liquid

  6. Collect the first fraction of the lower boiling point liquid

  7. Temperature rises again as the higher boiling point liquid vaporizes

  8. Thermometer plateaus at the boiling point of the higher boiling point liquid

  9. Collect the second fraction of the higher boiling point liquid
• If the two liquids have very similar boiling points, it is much harder to separate them and may require multiple rounds of fractional distillation
• Fractional distillation is not suitable for separating very large volumes of liquid, such as when refining crude oil
• Paper chromatography


  A separation technique used by scientists to separate substances in a mixture
• Paper chromatography is a physical process that does not involve chemical reactions and no new substances are made
• Stationary phase


  The paper, which does not move
• Mobile phase


  The solvent, which moves up the paper
• Paper chromatography procedure


  1. Draw pencil line at bottom of paper

  2. Put dots of substances on line

  3. Place paper in solvent

  4. Solvent moves up paper, dissolving and carrying substances

  5. Substances separate based on solubility
• A pure compound will produce a single spot in all solvents, while compounds in a mixture may separate into different spots
• Drawing the starting line in pencil is important because pen could dissolve in the solvent and move up the paper
• Paper chromatography can be used to identify compounds by calculating the RF value
• Nuclear model of atomic structure

  Most of an atom is empty space, with a positive nucleus containing most of the mass, and negative electrons at the edge
• Nuclear model


  • Electrons orbit the nucleus at specific distances (energy levels/shells)
  • Positive charge in nucleus due to protons
  • Nucleus also contains neutral particles called neutrons
• Radius of an atom is around 0.1 nanometer
• Radius of the nucleus is approximately 1 * 10^-14 m
• Nearly all the mass of the atom is found in the nucleus
• Relative charge


  Charge of one particle compared to another particle
• Relative charge of particles


  • Protons: +1
  • Neutrons: 0
  • Electrons: -1
• Atoms have no overall charge because the number of electrons equals the number of protons
• Relative mass


  Mass of one particle compared to another particle
• Relative mass of particles


  • Protons: 1
  • Neutrons: 1
  • Electrons: very tiny
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number


  The total number of protons and neutrons in the nucleus of an atom