Bonding, Structure and Properties of Matter

• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  Particles are oppositely charged ions - between non metals and metals
• Covalent bonding


  Particles are atoms which share pairs of electrons - between non metals
• Metallic bonding


  Particles are atoms which share delocalised electrons
• Ionic bonding occurs in compounds formed from metals combined with non-metals
• Covalent bonding occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding occurs in metallic elements and alloys
• Students should be able to explain chemical bonding in terms of electrostatic forces and the transfer or sharing of electrons
• Formation of an ionic compound

  1. Metal atom loses electrons to become positively charged ion

  2. Non-metal atom gains electrons to become negatively charged ion

  3. Ions have electronic structure of noble gas
• Ionic compound


  Giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions
• Representations of ionic compounds

  • Dot and cross diagrams
  • Two-dimensional stick diagrams
  • Three-dimensional stick diagrams
  • Ball and stick diagrams
  • Space-filling diagrams
• Ionic compounds


  • Have high melting and boiling points due to large amounts of energy needed to break strong bonds
  • Conduct electricity when melted or dissolved in water due to free movement of ions
• Covalent bond


  Bond formed when atoms share pairs of electrons
• Representations of covalent bonds

  • Dot and cross diagrams
  • Two-dimensional stick diagrams
  • Three-dimensional stick diagrams
• Substances with small covalent molecules

  • Usually gases or liquids with low melting and boiling points due to only weak intermolecular forces
  • Do not conduct electricity as molecules have no overall charge
• Polymers


  • Have very large molecules with strong covalent bonds between atoms
  • Relatively strong intermolecular forces make them solids at room temperature
• Substances with giant covalent structures

  • Solids with very high melting points as strong covalent bonds must be overcome
  • Examples are diamond, graphite, and silicon dioxide
• Metallic bonding


  Atoms arranged in regular pattern with delocalised electrons in outer shell that are free to move through whole structure
• Metals

  • Have high melting and boiling points due to strong metallic bonding
  • Atoms arranged in layers allowing metals to be bent and shaped
  • Metals are good conductors of electricity and thermal energy due to delocalised electrons
• States of matter


  • Solid
  • Liquid
  • Gas

  
• Melting and freezing


  Occur at melting point
• Boiling and condensing


  Occur at boiling point
• Particle theory model


  Particles represented by small solid spheres
• Stronger forces between particles result in higher melting and boiling points
• Limitations of simple particle theory model include no forces, all particles represented as solid spheres
• Chemical equation states of matter

  • (s) solid
  • (l) liquid
  • (g) gas
  • (aq) aqueous solution
• Diamond


  • Each carbon atom forms four covalent bonds in giant covalent structure, making it very hard with high melting point and non-conductive
• Graphite


  • Each carbon atom forms three covalent bonds, with one delocalised electron, forming layers with no bonds between layers
• Graphene


  Single layer of graphite
• Fullerenes


  Molecules of carbon atoms with hollow shapes, based on hexagonal rings which may also contain five or seven membered rings

  
• Carbon nanotubes


  Cylindrical fullerenes with very high length to diameter ratios
• Nanoscience


  Structures 1-100 nm in size, of the order of a few hundred atoms
• Nanoparticles


  Smaller than fine particles (PM2.5) which have diameters between 100-2500 nm
• As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10
• Nanoparticles may have properties different from the same materials in bulk due to their high surface area to volume ratio
• Applications of nanoparticles


  • Medicine
  • Electronics
  • Cosmetics and sun creams
  • Deodorants
  • Catalysts