bonding

• Key info


  • Covalent bonding is when electrons are shared between non-metal atoms
  • Single bond - each atom shares 1 pair of electrons
  • Double bond - each atom shares two pairs of electrons
• Structure of a giant covalent structure

  • Vibrations of atoms bonded together by strong covalent bonds (e.g. diamond)
• Polymers


  Small numbers of atoms group together into molecules with strong covalent bonds between the atoms
• Giant covalent structures are solid at room temperature, small molecules are liquid/gaseous, and large molecules are solid at room temperature
• Graphite


  • One carbon atom bonds to three others to form hexagonal rings
  • Delocalised electrons are free to move around the structure
• Hardness


  Soft, as the layers can slide over each other as they are not covalently connected
• Conductivity


  Conductive, as the delocalised electrons are free to move through the structure and carry charges
• Covalent Bonding


  Sharing of electrons between non-metal atoms
• Single Bond


  Sharing 1 pair of electrons between atoms
• Double Bond


  Sharing 2 pairs of electrons between atoms
• Covalent Bonding


  Typically occurs between non-metal atoms
• Ionic Bonding


  Transfer of electrons, typically between metal and non-metal atoms, forming oppositely charged ions
• Giant Covalent Structure


  A structure composed of many atoms bonded together by strong covalent bonds.
• Polymer


  A large molecule made up of multiple smaller molecules, composed of multiple atoms bonded together.
• Ionic Properties


  Static force of attraction between the opposing ions which are strongly held together, requires lots of energy to break
• Ionic conductivity


  • Conducts electricity when dissolved in water because the ions are free to move and carry charge
• Structure of giant ionic lattice

  Regular structure of positive and negative ions held together by the electrostatic force of attraction
• Metallic structure


  • Arrangement of positive metal ions surrounded by delocalised electrons
• Metallic properties


  • Pure metals are malleable because the layers can slide over each other
  • Good conductors of electricity and heat because delocalised electrons are free to move through the whole structure
  • High melting points because the electrostatic force of attraction between metal ions and delocalised electrons is strong so lots of energy is needed to break
• Alloy


  Mixture of a metal with atoms of different elements
• Structure of an alloy

  • Alloys are harder than pure metals because they have different sized atoms which disturb the layers so it prevents them from sliding over each other
• Difference between pure metals and alloys: pure metals have layers that can slide, alloys have no layers so no sliding, making them harder
• Graphene


  Single layer of graphite, has strong covalent bonds making it a strong material that can also conduct electricity, used in composites and high-tech electronics
• Fullerene


  Hollow cages of carbon atoms bonded together in one molecule as sphere or tube, held together by weak intermolecular forces so can slide over each other, conducts electricity
• Fullerene


  • Buckminsterfullerene - has 60 carbon atoms, can be used as lubricants and in drug delivery
• Nanotubes


  • Hollow cylinder of carbon atoms, have high tensile strength and conduct electricity, used in lubricants, drug delivery, and high-tech electronics
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• Microscope use


  1. Clip one side carefully onto one stage

  2. Ensure lowest-powered objective lens is over the slide

  3. Use the coarse adjustment knob to bring the stage up just below the lens

  4. Look down the eyepiece and gradually move the stage downwards using the coarse adjustment knob stop when the image is roughly in focus

  5. Bring the image into focus by adjusting the fine adjustment knob until a clear image is obtained

  6. Observe the image with a higher magnification, change the objective lens to a higher power and readjust the stage using the coarse and fine adjustment
• Enzyme effect of pH on amylase

  1. Place 2cm³ starch solution, 2cm³ amylase solution, and 2cm³ pH 5 buffer solution in 3 test tubes

  2. Place the test tubes in a water bath at 30°C for 10 mins

  3. Combine all solutions into one test tube and mix with a stirring rod

  4. Return the test tube to the water bath and start the stopwatch

  5. After 30 secs, use the stirring rod to add iodine until it turns orange, this means starch is no longer present

  6. Repeat with pH buffers 6, 7, 8
• Food tests


  1. Take the food sample and grind it with distilled water using a mortar and pestle

  2. Transfer the paste to a beaker and add more distilled water, stir so the chemicals in the food dissolve

  3. Filter the solution to remove food particles

  4. Test for starch by adding 3cm³ of food solution and a few drops of iodine solution (turns blue-black if starch is present)

  5. Test for sugars (glucose) by adding 2cm³ of food solution and 10 drops of Benedict's solution, then heating in a water bath (turns green, yellow, or brick red depending on amount of sugar)

  6. Test for proteins by adding 2cm³ of food solution and 2 drops of biuret solution (turns lilac if protein is present)

  7. Test for lipids by adding 2cm³ of food solution, a few drops of distilled water, and gently shaking (turns cloudy-white if lipids are present)
• Communicable diseases are caused by pathogens which spread from one organism to another
• Pathogens are microorganisms that cause infectious disease
• Types of pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• How bacteria make us ill

  1. Bacteria reproduce rapidly once inside the body

  2. Bacteria release harmful chemicals called toxins

  3. Toxins damage tissues and make us ill
• How viruses make us ill

  1. The virus invades the host cell

  2. The virus reproduces inside the host cell

  3. When the virus leaves the cell, the cell bursts open and dies