2. Bonding,structure and properties of matter

• Ions


  Charged particles - can be single atoms (e.g. C) or groups of atoms (e.g. N)
• Atoms forming ions


  Trying to get a full outer shell like a noble gas
• Formation of ions


  1. Atoms lose or gain electrons

  2. Charge on ion is same as number of electrons lost or gained
• Groups most likely to form ions

  • Group 1
  • Group 2
  • Group 6
  • Group 7
• Group 1 elements


  Form positive ions (cations)
• Group 2 elements


  Form positive 2+ ions
• Group 6 elements


  Form negative ions
• Group 7 elements


  Form negative ions
• Formation of ions


  • Sodium atom (Na) forms Na+ ion
  • Magnesium atom (Mg) forms Mg2+ ion
  • Chlorine atom (Cl) forms Cl- ion
  • Oxygen atom (O) forms O2- ion
• Ionic bonding


  • Transfer of electrons between metal and non-metal
  • Oppositely charged ions are strongly attracted to each other
• Ionic compounds


  • Have a regular lattice structure
  • Have high melting and boiling points
  • Can conduct electricity when molten or in aqueous solution
• Determining formula of ionic compound

  1. Count atoms of each element

  2. Balance charges to get overall neutral charge
• Ionic compound formula


  • Potassium oxide (K2O)
• Covalent bonding


  • Sharing of electrons between non-metal atoms
  • Atoms share electron pairs to fill their outer shells
• Covalent compounds


  • Have low melting and boiling points
  • Do not conduct electricity
• Covalent compounds


  • Ammonia (NH3)
  • Ethane (C2H6)
• Molecular formula shows number of atoms of each element in a molecule
• The 3D model of ammonia shows the atoms, the covalent bonds and their arrangement in space next to each other. But 3D models can quickly get confusing for large molecules where there are lots of atoms to include. They don't show where the electrons in the bonds have come from, either.
• You can find the molecular formula of a simple molecular compound from any of these diagrams by counting up how many atoms of each element there are.
• Ethane molecule


  • 2 carbon atoms
  • 6 hydrogen atoms
• Molecular formula


  Shows how many atoms of each element are in a molecule
• Simple molecular substances are made up of molecules containing a few atoms joined together by covalent bonds.
• Examples of simple molecular substances

  • Hydrogen
  • Oxygen
  • Methane
  • Chlorine
  • Nitrogen
  • Water
  • Hydrogen Chloride
• Substances containing covalent bonds

  • Usually have simple molecular structures
  • The forces within the molecules are held together by very strong covalent bonds
  • The forces of attraction between these molecules are very weak
• To melt or boil a simple molecular compound


  You only need to break the feeble intermolecular forces and not the covalent bonds
• Most molecular substances are gases or liquids at room temperature.
• As molecules get bigger

  The strength of the intermolecular forces increases, so more energy is needed to break them, and the melting and boiling points increase
• Molecular compounds don't conduct electricity, simply because they are not charged, so there are no free electrons or ions.
• In a polymer, lots of small units are linked together to form a long molecule that has a repeating structure.
• Polymers


  • All the atoms in a polymer are joined by strong covalent bonds
  • Instead of drawing out a whole long polymer molecule, you can draw the shortest repeating section, called the repeating unit
• To find the molecular formula of a polymer

  Write down the molecular formula of the repeating unit, and put an 'n' outside
• The intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to break them.
• In giant covalent structures, all the atoms are bonded to each other by strong covalent bonds.
• Giant covalent structures


  • Have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms
  • Don't contain charged particles, so they don't conduct electricity - not even when molten
• Main examples of giant covalent structures

  • Diamond
  • Graphite
  • Silicon dioxide (silica)
• Diamond


  Each carbon atom forms four covalent bonds in a rigid giant structure
• Graphite


  Each carbon atom forms three covalent bonds to create layers of hexagons, with one delocalised (free) electron
• Silicon dioxide (silica)

  What sand is made of, a giant structure of silicon and oxygen
• Graphene is a sheet of carbon atoms joined together in hexagons, just one atom thick.
• Graphene


  • The network of covalent bonds makes it very strong and incredibly light
  • Contains delocalised electrons so can conduct electricity through the whole structure