C5: Chemicals of the Natural Environment

1. Molecular Substances
   1. Molecular Diagrams
      1. Molecular Formula
         1. O2
         2. CH4
         3. Only shows number of atoms in a molecule
      2. Displayed Formula
         1. O=O
         3. Shows atoms and covalent bonds, so you can tell how they're joined together.
      3. 3-D model
         1. Shows the atoms, their covalent bonds and their arrangement in space next to each other.
   2. Molecular substances have LOW boiling and melting points.
   3. Gasses in the atmosphere are molecular because they contain atoms joined together in small molecules.
      1. Atoms within the molecules have a very strong covalent bonds.
         1. But have very weak forces of attraction between the molecules. Which is why they're all gasses or liquids at room temperature and have low melting and boiling points; because it takes little energy to separate the weak forces of attraction.
   4. Don't conduct electricity because there are no free electrons/charges.
   5. Most non-metal elements and compound form molecular substances.
2. Dry air is a mixture of gasses
   1. 21% Oxygen
   2. 78% Nitrogen
   3. 0.04% Carbon Dioxide
   4. 1% Argon

1. Atoms bond covalently to complete their outer shell. But rather than gaining or loosing electrons, atoms achieve a complete outer shell by sharing electrons.
   1. Hydrogen
      1. Needs just one electron to complete it's outer shell each atom bonds with another hydrogen atom.
      2. Which is why hydrogen exists as a diatomic molecule.
   2. Carbon Dioxide
      1. Carbon needs FOUR more electrons to complete it's outer shell, oxygen needs TWO.
         1. So a double covalent bond is formed, as the atoms share 2 electons.
2. Each atom involved has to make enough bonds to fill up it's outer shell.
3. Electrostatic attraction spurs the bonding.

Annotations:

• http://www.ocr.org.uk/Images/144862-question-paper-unit-a172-01-modules-c4-c5-c6-higher-tier.pdf (data sheet)

1. Flame Tests for Positive Ions
   1. Sodium, Na+
      1. Orange/yellow flame.
   2. Potassium, k+
      1. Lilac flame.
   3. Calcium, Ca2+
      1. Red flame.
   4. Copper, Cu2+
      1. Blue/Green flame.
2. A precipitate reaction is where two solutions react to form an insoluble solid compound, this is the precipitate.
   1. The colour of the insoluble hydroxide tells you which positive ion was in a solution.

1. All the water in earth and the compunds dissolved in it.
   1. The ocean is salty because many of the compounds are dissolved salts.
   2. Solid ionic compounds form crystals.
      1. A giant lattice of ions form beacuse of the strongly attracted oppositely charged ions. Ionic bonds are very strong chemical bonds between the ions.
         1. Ionic compounds have high melting and boiling points (molecular substances have low)
            1. Beacause forces of attraction are very strong, therefore it takes a lot of energy to overcome them. This makes them solids at room temperature.
      2. Ionic compounds conduct when molten or dissolved.
         1. Because the ions separate and are free to move.
            1. Therefore can carry and electric current.

1. Giant Covalent Structures
   1. Carbon
      1. Diamond
         1. The carbon atoms in diamond form FOUR covalent bonds.
         2. The carbon forms a very ridged, giant covalent structure.
         3. It is the hardest natural substance therefore an ideal cutting tool.
         4. High melting point because the covalent bonds are very strong. Diamond is insoluble.
         5. No free electrons therefore cannot conduct.
      2. Graphite
         1. Also made of carbon but has a different covalent structure.
         2. Each carbon atom only forms THREE covalent bonds.
            1. this makes graphite slippery thus useful as a lubricant because the layers are free to slide over each other.
            2. Also, because there are only three covalent bonds, the layers are held together loosely, this means they are able to be rubbed off onto paper.
         3. Has a high melting point.
         4. Graphite CAN conduct electricity because only 3 of carbon's 4 outer electrons are used in the bonding. There is 1 free electron per bond.
   2. Silicon Dioxide
      1. Most silicon and oxygen in the Earth's crust exits as the compound silicon dioxide.
      2. Each grain of sand is one giant silicon dioxide structure.
      3. High melting point
      4. Doesn't conduct electricty
2. Comprising of the crust and mantle, the lithosphere is made up of a mixture of minerals such as; silicon, oxygen and aluminium.
   1. Different types of rock contain different minerals and elements.
      1. e.g. the compound limestone (CaCo3) contains a lot of calcium (Ca)