SC7

• Covalent compounds:

  • low melting/boiling points
  • don't conduct electricity
  • soft solids

  Covalent bonds are formed when 2 atoms share electrons which is usually between gases like water (H2O), oxygen (O2) and methane (CH4)
• Simple Molecular compounds:

  • low melting/boiling points
  • don't conduct electricity
  • mostly insoluble

  A simple molecular bond is what holds multiple atoms together like hydrogen (H2) and ammonia (NH3)
• Covalent and simple molecular compounds:

  • Low melting/boiling points as they have weak intermolecular forces so little energy is needed to break bonds
  • Poor conductors of electricity as they don't have a charge for electricity to travel through
• Polymers:

  • large molecules (giant covalent)
  • consist of many atoms that have strong covalent bonds which forms a chain
  • strong intermolecular forces so it has a high melting/boiling point
• Allotropes - different structural forms (molecules) of the same atom such as carbon with fullerene, graphene, graphite and diamond
• Giant Covalent Structure - the atoms are joined up by covalent bonds over huge (variable) numbers (e.g. diamonds)
• Simple Molecular Structure - contain only a few atoms held together by covalent bonds (e.g. CO2)
• Fullerenes:

  • carbon atoms are bonded to 3 others
  • spherical and hollow structure (nanotubes)
  • weak intermolecular forces mean low melting/boiling points and being soft/slippery
• Graphene:

  • one atom thick means light and transparent
  • carbon atoms rearranged in hexagons
  • high melting/boiling points from strong covalent bonds
  • conducts electricity with delocalised electrons
• Graphite:

  • giant covalent structure
  • made of layers of graphene so has weak intermolecular forces
  • conducts electricity with delocalised electrons
  • good lubricant as layers slide easily
• Diamond:

  • giant covalent structure with a tetrahedral/pyramid shape
  • lattice arrangement means a rigid structure make it very hard
  • carbon atoms are covalently bonded to 4 others
  • no delocalised electrons so cannot conduct electricity
• Metallic Bonding - the electrostatic attraction between the positive metal ions and the negative delocalised electrons

  • attraction is strong so metals have high melting/boiling points
• Pure Metals:

  • all atoms are the same size and have 1-3 outer shell electrons
  • outer shell electrons are lost and free to randomly move which creates a sea of electrons around positive ions
  • malleable as layers of positive ions slide over each other easily
  • sea of electrons hold ions together so it changes chape instead of breaking

  When potential difference (voltage) is applied between two points, electrons flow to the positive side which transfers energy and forms an electrical current - more delocalised electrons means better conductivity
• Typical Properties of Metals:

  • solids with high melting/boiling points
  • shiny (when polished)
  • malleable
  • high density
  • good conductors of electricity
• Typical Properties of Non-Metals:

  • solids/liquids/gases with low melting points
  • not usually shiny (when solid)
  • brittle (when solid)
  • low density
  • poor conductors of electricity
• Ionic:

  • found in most compounds containing metal and non-metal atoms
  • bonds formed by loss/gain of electrons
  • complete outer shells
  • oppositely charged ions that attract each other
  • lattice structure
  • many are soluble in water
• Simple Molecular (Covalent):

  • found in most non-metal elements/compounds
  • covalent bonds formed when atoms share pairs of electrons
  • structure of small, distinct groups of atoms
  • few are soluble in water
• Giant Covalent:

  • found in a few non-metal elements/compounds
  • insoluble in water
  • covalent bonds held in a lattice structure
• Metallic:

  • found in all metals
  • giant lattice structure of positive ions in a sea of delocalised electrons
  • insoluble in water
• Substances with high melting/boiling points have strong bonds that need a lot of heat energy to break.

  Low melting/boiling points show weak inter-molecular forces that need to be overcome

  Substances that conduct electricity have ions that can freely move
• Dot and Cross Diagram:

  • shows how electrons are shared (advantage)
  • doesn't show structure formed (disadvantage)
  • suggests electrons are different (disadvantage)
• Metallic Diagram:

  • shows metal ions in lattice (advantage)
  • explains electricity conduction (advantage)
  • doesn't show ions vibrating (disadvantage)
• 3D Ball and Stick Diagram:

  • shows which atoms are joined (advantage)
  • shows structure shape (advantage)
  • atoms are too far apart (disadvantage)
  • inaccurate as there are no actual sticks (disadvantage)