bonding and structure

• Compounds


  Substances in which 2 or more elements are chemically combined
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding


  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Ionic bonding formation


  1. Metal atoms lose electrons to become positively charged ions

  2. Non-metal atoms gain electrons to become negatively charged ions

  3. Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain full outer shell of electrons
• Ionic compound example


  • Sodium chloride (salt)
• Ionic compounds


  Giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions
• Covalent bonding


  • Atoms share one or more pairs of electrons
  • Small molecules have strong covalent bonds within their molecules
  • Polymers are large covalently bonded molecules
  • Giant covalent structures consist of many atoms covalently bonded in a lattice structure
• Metallic bonding


  • Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
  • Delocalised electrons are free to move through the structure
  • Delocalised electrons are shared through the structure so metallic bonds are strong
• The three states of matter

  • Solid
  • Liquid
  • Gas
• Melting and freezing


  Take place at the melting point
• Boiling and condensing


  Take place at the boiling point
• Particle theory


  • The amount of energy needed to change state depends on the strength of the forces between the particles
  • The nature of the particles involved depends on the type of bonding and the structure of the substance
  • The stronger the forces between the particles the higher the melting point and boiling point of the substance
• State symbols


  Solid (s), liquid (l), gas (g), aqueous (aq)
• Properties of ionic compounds

  • Have regular structures (giant ionic lattices) with strong electrostatic forces of attraction in all directions
  • Have high melting and boiling points
  • Conduct electricity when melted or dissolved in water but not when solid
• Properties of small molecules

  • Usually gases or liquids with low boiling and melting points
  • Have weak intermolecular forces between the molecules
  • Larger molecules have higher melting and boiling points
  • Don't conduct electricity
• Polymers


  • Have very large molecules
  • Atoms in the polymer molecules are linked by strong covalent bonds
  • Intermolecular forces between polymer molecules are relatively strong so they are solids at room temperature
• Giant covalent structures


  • Substances with very high melting points where all atoms are linked by strong covalent bonds
• Giant covalent structures


  • Diamond, graphite, silicon dioxide
• Properties of metals and alloys


  • Metals have giant structures of atoms with strong metallic bonding
  • Most metals have high melting and boiling points
  • Layers of atoms can slide over each other
  • Alloys are harder than pure metals because different sized atoms distort the layers
• Metals as conductors


  Good conductors of electricity and thermal energy due to delocalised electrons
• Diamond


  • Each carbon is joined to 4 other carbons covalently
  • Very hard, high melting point, does not conduct electricity
• Graphite


  • Each carbon is covalently bonded to 3 other carbons, forming layers with weak intermolecular forces between them
  • Soft and slippery
  • One electron from each carbon atom is delocalised, allowing it to conduct electricity
• Graphene


  • Single layer of graphite
  • Very strong and elastic due to tight covalent bonding within layers
• Fullerenes


  • Molecules of carbon atoms with hollow shapes based on hexagonal rings, may also contain 5 or 7 membered rings
  • First discovered was Buckminsterfullerene (C60) with a spherical shape
• Carbon nanotubes


  • Cylindrical fullerenes with very high length to diameter ratios
  • Useful for nanotechnology, electronics and materials
• Nanoparticles


  • 1-100 nanometers across, containing a few hundred atoms
  • Have different properties to the 'bulk' chemical due to high surface area to volume ratio
• Uses of nanoparticles


  • Good catalysts
  • Highly selective sensors
  • Stronger, lighter building materials
  • New cosmetics
  • Lubricant coatings
  • Small electrical circuits
• Possible disadvantages of nanoparticles: there are some concerns that they may be toxic to people and able to enter the brain from the bloodstream