C5- Chemicals of the Natural Environment

C5- Chemicals of the Natural Environment

1. Dry Air Composition

   • Oxygen- 21%
   • Nitrogen- 78%
   • Argon- 1%
   • Carbon Dioxide- 0.04%

2. Molecular substances

   • Held together by strong covalent bonds
   • Forces of attraction between molecules are weak
   • Low melting and boiling points
     • You only need a bit of energy to overcome forces between molecules
   • Don't conduct electricity
   • Most non-metal elements are molecular

3. Covalent Bonding

   • Sharing electrons
   • Provides atoms with a full outer shell of electrons
   • Each covalent bond provides one extra shared electron for each atom
   • Atoms bond due to the electrostatic attraction between the positive nuclei and negative electrons shared between them
   • Hydrogen- H2
     • Hydrogen needs one electron to fill its outer shell
       • So two (h2) hydrogen atoms share their outer electron so they each have a full shell and a covalent bond is formed
   • Carbon Dioxide, Co2
     • Carbon needs four more electrons to fill its outer shell, oxygen needs two
       • Two covalent bonds are formed
         • A double covalent bond has two shared pairs of electrons

4. Chemicals in the Hydrosphere

   • Hydrosphere consists of water on Earth
     • Compounds dissolved in water
     • These compounds are ionic compounds called salts
       • Ionic compounds are made of charged particles called 'ions'
         • 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
         • 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
         • 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

5. Identifying Positive Ions

   • 1.) Flame tests- Compounds of some metals give characteristic colours when heated. You can use these colours to detect and identify different ions
   • 2.) Precipitation Reactions
     • This is where two solutions react to form an insoluble compound called a precipitate
       • Metal hydroxides are insoluble and form a precipitate in a solution where an alkali is added
         • They give off characteristic colours- allowing you to idenitfy what metal ion was in the compound
   • 3.) Ionic Equations- show the useful bit of reactions

6. Identifying negative ions

   • Hydrochloric acid can detect carbonates
     • Carbonates will fizz if they have hydrochloric acid in them
       • Carbon dioxide turns limewater cloudy
         • If water turns cloudy, you've idenitifed a carbonate ion
   • To identify a sulfate ion add dillute HCl followed by barium chloride solution
     • A white precipitate of barium sulfate means the original compound was a sulcate
   • Halide ions will give a coloured solution when mixed with dilute nitric acid