C3

• Bonds:

  • Ionic (metal + non-metal) - attraction between oppositely charged ions
  • Covalent (non-metal + non-metal) - 2 atoms sharing 1 or more pairs of electrons
  • Metallic (metal + metal) - attraction between positively charged ions and negatively charged DELOCALISED electrons (found in alloys)
• Ionic bonds:

  • positive ions have lost electrons, a.k.a. cations, and usually from groups 1 and 2
  • negative ions have gained electrons, a.k.a. anions, and usually from group 7
  • ions can contain multiple elements
  • group 8 (noble gases) don’t form ionic compounds because of their already stable outer shell
  • ionic compounds are held together by strong electrostatic forces
• Covalent bonds:

  • when 2 non-metals share a pair of electrons
  • strong because electrons are attracted to the nucleus of both atoms
  • can be:

  *small molecules e.g. water

  *large molecules e.g. polymers like polyester/silk

  *giant covalent structures e.g. diamonds

  • represented by dot and cross diagrams
  • can make single, double, or triple bonds
• Giant covalent structures:

  • Diamond - made out of carbon and no delocalized electrons so does NOT conduct electricity; used for drill bits and jewellery
  • Graphite - is made out of carbon and has 1 delocalized electron so DOES conduct electricity; hexagonal sheets in layers with weak intermolecular forces; are used as lubricants
  • Graphene - 1 sheet/layer of graphite with strong covalent bonds; used for transparent electrical appliances
• Giant Covalent Structures:

  • Buckminster Fullerene - made of carbon (C60); used during drug delivery
  • Carbon Nanotubes - 1 sheet/layer of graphene folded in on itself as a tube; lightweight so good building material
  • Silicon dioxide - more commonly known as glass; is made of silicone and oxygen; and has a high melting point
• Metallic bonding:

  • electrostatic attraction between delocalized electrons and positively charged ions
  • happens in alloys - in pure metals, the layers slide but in alloys, they don’t
  • ions (cations) are in a regular lattice in a “sea” of delocalized electrons
  • delocalized electrons are free to move and carry charge AND kinetic energy because the metals have a small number of electrons in their outer shells
• States of matter:

  • solid particles vibrate around a fixed position, have a fixed shape and volume, and when heated, particles vibrate more intensely
  • liquid particles are very close together but move past each other, have a fixed volume but not shape, and when heated the speed of particles increases
• States of matter:

  • gas particles are far apart and move in random directions, do not have a fixed shape or volume, and when heated the speed of particles increases
  • usually represented by a ‘particle’ model, which has disadvantages such as it doesn’t show the forces between particles, shows them as a sphere when they are not, and shows them as solid when they are not
• Changing state:

  • when particles gain or lose energy because of heating or cooling
  • heating causes a substance to melt or boil
  • cooling causes a substance to condense or freeze
  • amount of energy required to change a substance’s state depends on whether its forces between particles are weak or strong
  • (s) used for solids, (l) used for liquid, (g) used for gas, (aq) used for aqueous solutions, where substances are dissolved in a solution
• Nanotechnology:

  • science of molecules that are 1 of 1 x10^-9 metres in size
  • nanoparticles have a large surface area to volume-ratio
  • they increase the rate of reaction; used as catalysts
  • used in sun creams, self-cleaning coated windows, and anti-bacterial e.g. socks
  • risks include lack of knowledge of long-term risks and not fully understood; could be toxic