C5

C5

1. Chemicals in the atmosphere

   • Molecular Substances
     • Molecular Diagrams
       • Displayed Formula
         • O=O
         • Shows atoms and covalent bonds, so you can tell how they're joined together.
       • 3-D model
         • Shows the atoms, their covalent bonds and their arrangement in space next to each other.
     • Molecular substances have LOW boiling and melting points.
     • Gasses in the atmosphere are molecular because they contain atoms joined together in small molecules.
       • Atoms within the molecules have a very strong covalent bonds.
         • 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.
     • Don't conduct electricity because there are no free electrons/charges.
     • Most non-metal elements and compound form molecular substances.
   • Dry air is a mixture of gasses
     • 21% Oxygen
     • 78% Nitrogen
     • 0.04% Carbon Dioxide
     • 1% Argon

2. Covalent Bonding: Sharing Electrons

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

3. Identifying Ions

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

4. Chemicals in the Hydrosphere

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

5. Chemicals of the Lithosphere

   • Giant Covalent Structures
     • Carbon
       • Diamond
         • The carbon atoms in diamond form FOUR covalent bonds.
         • The carbon forms a very ridged, giant covalent structure.
         • It is the hardest natural substance therefore an ideal cutting tool.
         • High melting point because the covalent bonds are very strong. Diamond is insoluble.
         • No free electrons therefore cannot conduct.
       • Graphite
         • Also made of carbon but has a different covalent structure.
         • Each carbon atom only forms THREE covalent bonds.
           • This makes graphite slippery thus useful as a lubricant because the layers are free to slide over each other.
           • 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.
         • Has a high melting point.
         • 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.
     • Silicon Dioxide
       • Most silicon and oxygen in the Earth's crust exits as the compound silicon dioxide.
       • Each grain of sand is one giant silicon dioxide structure.
       • High melting point
       • Doesn't conduct electricty
   • Comprising of the crust and mantle, the lithosphere is made up of a mixture of minerals such as; silicon, oxygen and aluminium.
     • Different types of rock contain different minerals and elements.
       • e.g. the compound limestone (CaCo3) contains a lot of calcium (Ca)

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