C2

• Metallic bonding:

  Metals form a lattice (grid) of ions surrounded by a 'sea' of delocalised electrons. As these electrons are free to move, metals are good conductors of electricity and heat.
• Ionic bonding:

  How metals bond to non-metals.

  Metal atoms donate electrons to non-metals to form ions.

  Dot and cross diagrams show the electrons on the outer shells.

  Metals always end up with an empty outer shell, non-metals with 8 electrons.

  The charges of all ions in an ionic compound must add up to 0.
• Ions are arranged in a lattice of repeating units of positive and negative ions. These form a crystal.
• Ions can conduct electricity when molten or in solution (dissolved). This is because the ions are free to move in these states, and they can carry charge.
• Ionic substances have high melting/boiling points due to the strong ionic bonds (as the ions have strong electrostatic forces between them).
• Ionic compounds are also called salts.
• Positive ions are known as cations.
• Negative ions are called anions.
• Covalent bonding is how non-metals bond to each other.

  Atoms share electrons to gain full outer shells.
• In covalent bonding, we can draw a dot and cross diagram or the structural formula, with a line representing each bond.

  The number of electrons an atom needs = the number of bonds it makes.
• Simple covalent structures are molecules with a small number of atoms. They have low boiling points due to weak intermolecular forces that need to be overcome.
• Giant covalent bonding results in structures that consist of repeating units ot atoms to make what are essentially giant molecules e.g diamond or silicon dioxide.

  Very high melting points as you would have to break the covalent bonds.
• Allotropes are structures made of the same element but arranged differently.
• Diamond is an allotrope of carbon and one of the hardest known substances due to very strong bonds.
• Graphite consists of layers of carbons with 3 bonds each in a hexagonal structure. The delocalised electrons form weak bonds between layers. Can conduct electricity as these electrons can move.

  Layers can slide past each other.
• Alloys are mixtures of metals: different size atoms disrupt the lattice, so layers cannot slide over each other easily - strong!
• Graphene is one layer of graphite.
• Fullerenes/nanotubes are used for electronics, composites and medical purposes. Buckminster fullerene is a spherical football-like structure consisting of 60 carbon atoms each.
• Nanoparticles: 1-100nm
• Fine particles: 100-2500nm
• Coarse particles e.g dust: >2500 nm
• Fullerenes are useful due to high surface to volume ratio, so fewer needed for purpose.

  Double the length = half the ratio.