Topic 1

• Metallic bonding Structures and Properties


  • Conduct heat
  • Conduct electricity
• Metallic bonding


  Metal beams bond together to carry electrical charge through the structure
• Ionic bonding


  Bonding between metal and non-metal atoms
• Ionic bonding example


  • Na & Cl
• Ionic bonding diagram


  1. [Na] [Cl] dot and cross diagram

  2. Cl will have 8 full outer shell electrons
• Covalent bonding


  Bonding between non-metals where atoms share electrons to fill their outer shells
• Covalent bonding


  Atoms share a pair of electrons
• Covalent bonding example


  • HCl
• Diamond


  • Each carbon bonded to 4 others
  • Does not conduct electricity
  • Used in drill bits
• Graphite


  • Bonded to 3 carbons
  • Conducts electricity
  • Used in pencils
• Molecules with double bonds

  Delocalised electrons
• Ionic Bonding has high melting point due to the strong bonds and strong electrostatic bonds
• Metals are good conductors because they have delocalized electrons that can move freely through the lattice structure.
• The boiling points of ionic compounds increase with increasing size of the anion or cation due to stronger intermolecular forces between larger molecules.
• Non-metals do not conduct electricity as their atoms are held together by covalent bonds, which prevent the flow of electrons.
• Covalent compounds generally have low melting points compared to ionic or metallic substances because the forces holding them together are weaker.
• Covalent bonding is weaker than ionic bonding, resulting in lower melting and boiling points compared to ionic substances.
• In covalent bonding, there is no overall charge on the molecule, while in ionic bonding, there is a net positive charge on one atom and a negative charge on another.
• Covalent bonding


  When non-metals share electrons
• Covalent bonds


  • Strong bonds
  • Giant covalent bonds (e.g. diamond, graphite)
  • Ionic bonding
• Properties of covalent bonds


  • Low melting and boiling points because of weak intermolecular forces
  • Do not conduct electricity
• Ionic bonding


  • Occurs between metals and non-metals
  • Electrostatic attractions between oppositely charged ions
  • Ions form a giant ionic lattice
• Metal ions


  Form a positively charged ion by losing electrons
• Non-metal atoms


  Gain electrons and become negatively charged
• Metallic bonding


  • The electrons in the outer shell are free to move and consist of delocalized electrons
  • The electrons can slide over each other causing metals to be malleable and ductile
  • High melting and boiling points
• Properties of ionic compounds


  • High melting and boiling points because of strong electrostatic attraction
  • When solid, cannot conduct electricity as ions are fixed in place
  • When molten, can conduct electricity as ions are free to move
• Giant Covalent Structures


  • Carbon allotropes
• Diamond Structure


  Each Carbon is bonded to 4 other Carbons
• Diamond


  • Very hard
  • High melting point
  • Doesn't conduct electricity
• Graphite Structure


  • Covalently bonded to 3 Carbons, forming layers of hexagonal rings
  • Layers can slide over each other due to no covalent bonds between layers
• Graphene


  Single layer of graphite
• Graphene


  • Useful properties for electronics
• Fullerenes


  Molecules of carbon atoms with hollow spaces
• Nanoparticles


  • Can be used as carriers to deliver drugs in the body
  • Nano silver used in wound dressings to prevent infections
  • Nano-scale titanium dioxide in sunscreen to block UV light
• Smart Materials


  • Shape memory polymers return to original shape when heated
  • Thermochromic mugs change colour at certain temperatures
  • Photochromic pigments in sunglasses change colour in light
• Polymers


  Can gel and absorb large amounts of water, e.g. nappies, fake snow
• Problems with nanoparticles include they can enter the bloodstream and their long-term effects are unknown