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MODULE C5: CHEMICALS OF THE NATURAL
ENVIRONMENT
Atmosphere• Molecular
elements (e.g. oxygen, nitrogen, ozone) and compounds (e.g.carbon dioxide, water)
• Monoatomic elements (e.g. argon)
hydrosphere
• Mainly water plus…
• Solution of ionic compounds (e.g. sodium chloride)
Q. Give the chemical symbols and state symbols for all the chemicals above.
PropertiesMolecular
compoundsIonic
compoundsMade from Two or more non-metal
atoms bondedMetal ions with non metal ions
Electrical properties
Insulators (no ions!) Conduct only when molten or dissolved in water
Forces holding them
together
Strong covalent bonds within the molecule but weak forces between molecules
Strong attractions between oppositely charged ions
Melting and boiling points
Low… found as gases at room temperature
High… found as solids or in solution
Formulae of salts• Metal ions (+) combine with non-metal
ions (-) to form neutral compounds.
• The formula of magnesium oxide is MgO
• The formula of sodium oxide is Na2O
Mg 2+
Mg 2+
Mg 2+
Mg 2+
Mg 2+
Mg 2+
O 2-
O 2-
O 2-
O 2-
O 2-
Mg 2+
O 2-
Na + O 2-
Na +
O 2-
O 2-
O 2-
O 2- O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
O 2-
Find the formula of… aluminium with fluorine,
calcium with chlorine, sulphur with potassium
The group number of the atom
can tell us which ion it will
form..
group ion
1 1+
2 2+
3 3+
4 None
5 3-
6 2-
7 1-
0 None
Lithosphere• Made of the crust and
upper mantle• Composed of minerals
e.g. quartz containing silicon dioxide found in granite and sandstone
• Rich in the atoms of silicon, oxygen and aluminium
Treasures of the Earth:
Gemstones for beauty, hardness, rarity
Chemical Brothers• Carbon dioxide and silicon dioxide are both covalently bonded
compounds but with very different physical properties
Carbon dioxide Silicon dioxide
Molecular structure (limited covalent bonding)
Giant structure (more extensive covalent bonding)
Low melting point High melting point
insulator Semi-conductor
gas Hard solid
Soluble in water Insoluble in water
negatively charged electrons are attracted to the positively charged nuclei to form strong covalent bonds
Extracting metals• For zinc, iron and copper (fairly un-reactive metals)
the ore (often an oxide) is mined, concentrated then the metal is extracted by heating with carbon
Copper oxide + carbon copper + carbon dioxide
lost oxygen gained oxygen
When oxygen is lost: REDUCTION
When oxygen is gained: OXIDATION
Re-write the equation above using symbols (chemical and state symbols!)
Write out the equivalent equation for iron (III) oxide (where iron has a 3+ charge)
Extracting reactive metals• The oxides of the more reactive metals are very stable so they
require large amounts of energy supplied by electricity in order to extract the metal. The electricity decomposes the compound into simpler substances.
Electrolyte: aluminium oxide (bauxite) with cryolite added
… in more detail• The cryolite
makes the aluminium oxide (bauxite) easier to melt so the ions in it are free to move to each electrode to become neutral atoms
Al 3+
Al 3+
Al 3+
O 2-
O 2-
O 2-
cathodeanode oxygen
gas released
Molten aluminium metal drops to the bottom
Use an ionic equation to show what happens at each electrode
Metals• The typical properties of high melting/
boiling points, high strength, malleable and conduction of heat/ electricity can all be explained by their structure
M + M +
M +
M +M + M +
M +
M + M +
Giant structure held together by ionic bonding
Metal ions in a lattice
Sea of electrons (free to move)
Environmental issues• The (i) mining, (ii) extraction,
(iii) transport, (iv) maintenance and (v) disposal of metals all have an impact on the environment.
• For each stage above suggest how it may affect the surroundings