C5- Chemicals of the Natural Environment

Dry Air Composition
1. Oxygen- 21%
2. Nitrogen- 78%
3. Argon- 1%
4. Carbon Dioxide- 0.04%
Molecular substances
1. Held together by strong covalent bonds
2. Forces of attraction between molecules are weak
3. Low melting and boiling points
  1. You only need a bit of energy to overcome forces between molecules
4. Don't conduct electricity
5. Most non-metal elements are molecular
Covalent Bonding
1. Sharing electrons
2. Provides atoms with a full outer shell of electrons
3. Each covalent bond provides one extra shared electron for each atom
4. Atoms bond due to the electrostatic attraction between the positive nuclei and negative electrons shared between them
5. Hydrogen- H2
  1. Hydrogen needs one electron to fill its outer shell
    1. So two (h2) hydrogen atoms share their outer electron so they each have a full shell and a covalent bond is formed
6. Carbon Dioxide, Co2
  1. Carbon needs four more electrons to fill its outer shell, oxygen needs two
    1. Two covalent bonds are formed
      1. A double covalent bond has two shared pairs of electrons
Chemicals in the Hydrosphere
1. Hydrosphere consists of water on Earth
  1. Compounds dissolved in water
  2. These compounds are ionic compounds called salts
    1. Ionic compounds are made of charged particles called 'ions'
      1. Ions with opposite charges are strongly attracted to each other
        You get a massive giant lattice of ions built up
        A single crystal of salt is one ionic lattice
      2. They have high melting and boiling points
        The forces of attraction are strong, so it requires a lot of energy to break them
        They are solid at room temperature
      3. When an ionic compound dissolves, the ions seperate and a free to move in solution
        This means they can carry an electric current or conduct electricity
        Ionic compounds conduct electricty when dissolved or molten (melted) because the electrons are free to move
Identifying Positive Ions
1. 1.) Flame tests- Compounds of some metals give characteristic colours when heated. You can use these colours to detect and identify different ions
2. 2.) Precipitation Reactions
  1. This is where two solutions react to form an insoluble compound called a precipitate
    1. Metal hydroxides are insoluble and form a precipitate in a solution where an alkali is added
      1. They give off characteristic colours- allowing you to idenitfy what metal ion was in the compound
3. 3.) Ionic Equations- show the useful bit of reactions
Identifying negative ions
1. Hydrochloric acid can detect carbonates
  1. Carbonates will fizz if they have hydrochloric acid in them
    1. Carbon dioxide turns limewater cloudy
      1. If water turns cloudy, you've idenitifed a carbonate ion
2. To identify a sulfate ion add dillute HCl followed by barium chloride solution
  1. A white precipitate of barium sulfate means the original compound was a sulcate
3. Halide ions will give a coloured solution when mixed with dilute nitric acid

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C5- Chemicals of the Natural Environment

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