C3 - Structure and Bonding

• The three states of matter

  • Solids
  • Liquids
  • Gases
• Solids


  • Particles packed closely together and vibrate around fixed positions
• Liquids


  • Particles close together but can slip and slide over each other in random motion
• Gases


  • Particles have, on average, lots of space between them and zoom around randomly
• Melting and boiling


  Energy transferred from the surroundings to the substance
• Freezing and condensing


  Energy transferred from the substance to the surroundings
• The simple particle model of solids, liquids, and gases is useful but has its limitations because the atoms, molecules, and ions that make up all substances are not solid spheres with no forces between them
• Elements


  React together to form compounds by gaining or losing electrons or by sharing electrons
• Elements that can form ionic compounds

  • Group 1
  • Group 2 (forming 2+ ions)
  • Group 6 (forming 2- ions)
  • Group 7
• Ionic compounds


  • Held together by strong forces of attraction between their oppositely charged ions
  • This is called ionic bonding
• Ionic compounds


  • High melting points because it takes a lot of energy to break the many strong ionic bonds, operating in all directions, that hold a giant ionic lattice together
  • All solids at room temperature
• Ionic compounds


  • Conduct electricity when molten or dissolved in water because their ions can then become mobile and can carry charge through the liquid
• Covalent bonds


  Formed when atoms of non-metals share pairs of electrons with each other
• Each shared pair of electrons is a covalent bond
• Many substances containing covalent bonds consist of simple molecules but some have giant covalent structures
• Substances made up of simple molecules

  • Have low melting points and boiling points
  • The forces between simple molecules are weak
  • These weak intermolecular forces explain why substances made of simple molecules have low melting points and boiling points
  • Have no overall charge, so they cannot carry electrical charge
  • Therefore, substances made of simple molecules do not conduct electricity
• Models are used to help understand bonding but each model has its limitations in representing reality
• Substances with giant covalent structures

  • Have very high melting points and boiling points
• Graphite


  • Contains giant layers of covalently bonded carbon atoms
  • No covalent bonds between the layers, so they can slide over each other, making graphite soft and slippery
• Diamond


  • Carbon atoms have a rigid giant covalent structure, making it a very hard substance
• Graphite

  • Can conduct electricity and thermal energy because of the delocalised electrons that can move along its layers
• Carbon


  • Also exists as fullerenes, which can form large cage-like structures and tubes, based on hexagonal rings of carbon atoms
• The fullerenes are finding uses as a transport mechanism for drugs to specific sites in the body, as catalysts, and as reinforcement for composite materials
• Graphene is a single layer of graphite and so is just one atom thick. Its properties, such as its excellent electrical conductivity, will help create new developments in the electronics industry in the future
• Metals


  • Atoms closely packed together and arranged in regular layers
  • Metallic bonding is positively charged metal ions, which are held together by electrons from the outermost shell of each metal atom
  • These delocalised electrons are free to move throughout the giant metallic lattice
• Metals


  • Can be bent and shaped because the layers of atoms (or positively charged ions) in a giant metallic structure can slide over each other
• Alloys


  • Harder than pure metals because the regular layers in a pure metal are distorted by atoms of different sizes in an alloy
• Metals


  • Delocalised electrons enable electricity and thermal energy to be transferred through a metal easily
• Nanoscience


  The study of small particles that are between 1 and 100 nanometres in size
• Nanoparticles


  • May have properties different from those for the same materials in bulk because they have a high surface area to volume ratio, with a high percentage of their atoms exposed at their surface
• Nanoparticles may result in smaller quantities of materials, such as catalysts, being needed for industrial processes
• New developments in nanoparticulate materials are very exciting and could improve many aspects of modern life
• The increased use of nanoparticles needs more research into possible issues that might arise in terms of health and the environment