1. Chemicals of the Natural Environment
C5 Revision
Chemicals of the Natural Environment

2. Objective
To revise the whole of C5

3. By the end of this lesson…..

4. Three parts of the Earth
Core
Mantle
Crust

5. The four spheres… Lithosphere: crust and upper mantle
Hydrosphere: Oceans and rivers
Atmosphere: Layer of air around the Earth
Biosphere: sphere of life

6. Chemicals of the atmosphere
78% N2
21% O2
1% Ar
0.03% CO2
Small amounts water vapour
All chemicals are gases – low melting and boiling points

7. Molecules
Most of the gases in the atmosphere consist of small molecules
Argon exists as single atom
Attractive forces between molecules weak – gases – moving too quickly

8. Bonds
Small molecules such as O2 or H2 do not split up unless at extremely high temperatures
Very strong bonds between atoms

9. Different bonds
Single bonds
Double bonds

10. Covalent Bonding
Non-metal atoms combine to form molecules – share electrons in their outer shells.
Held by electrostatic attraction between two nuclei and shared pair electrons

11. Chemicals of the Hydrosphere
Water has special properties:
Liquid at room temperature, even though has a smaller mass than the gases in atmosphere.
Melts at 0oC and boils at 100oC
Water molecules have a greater tendency to stick together.
Contracts until 0oC, then starts to expand – important in nature.

12. Good Solvent Good solvent for salts
Most common salts do not dissolve ions, but water does.
Does not conduct electricity, therefore does not contain charged particles free to move

13. Water molecules Three atoms appear at an angle
The hydrogen region has a slight positive charge
The oxygen region contains a slight negative charge

14. Water Molecule
The angle is due to the fact that the electrons are not evenly shared.
Oxygen has a greater share which explains the charges on each side of the molecule.
Overall they are still electrically neutral.

15. Small Charges
The small charges on opposite sides of the molecule cause slightly stronger attractive forces between them.
Also help water dissolve ionic compounds by attracting the ions out of their crystals.
Ice is less dense than water because of the molecules angular shape. They tend to line up in a very open structure.

16. Why is the sea salty?
Soluble chemicals carried from rocks to sea in water cycle.
Main chemical in sea sodium chloride
Built up over millions of years.
Most of compounds are salts – positive metal ions and negative non-metal ions.

17. Lithosphere Top part of lithosphere is crust
Rocks include boulders, stones and pebbles

18. Rocks.. Rocks are made of one or more minerals
Minerals are naturally occurring chemicals.
Can be elements such as gold and silver
More commonly compounds, such as silicon dioxide, calcium carbonate etc

19. Sandstone
Made of mainly one mineral
Silicon dioxide

20. Limestone
Made mainly of calcium carbonate

21. Granite
Mixture of quartz, feldspar and mica

22. Lithosphere
Two most common elements in lithosphere are oxygen and silicon.
These are abundant so form the major types of minerals, such as silicon dioxide.

23. Evaporite minerals Sea water contains lots of dissolved chemicals.
When evaporates ionic compounds crystallise Rock salt – Halite is one example.
Minerals formed this way are called evaporites – laid down millions of years ago

24. Ionic Bonding
Ions held together strongly by the opposite charges of their ions
E.g. Cl- and Na+
The structure is called a giant ionic structure.
Takes lots of energy to break down

25. Silica Consists of silicon dioxide Commonest form is quartz
One silicon to four oxygens
Form a 3D giant covalent
structure
Strong and rigid

26. Silicon dioxide Very Hard – used as abrasive
High mp and bp – linings for furnaces and high temp glassware
Insoluble in water – building
Electrical Insulator – silica glass used as insulator

27. Biosphere Biochemicals – Carbon, hydrogen, oxygen
Carbon is base of all living things:
Can form chains by joining to themselves
Forms four strong covalent bonds so other atoms can join
Means can make a variety of compounds.
Most are polymers

28. Proteins Hair skin and muscle. Enzymes Polymers made from amino acids
20 different amino acids

29. Proteins from amino acids

30. Carbohydrates Carbon Oxygen Hydrogen Sugars such as glucose
Photosynthesis produces glucose
Glucose very soluble

31. Nucleic Acids DNA and RNA are nucleic acids
Molecules that carry the genetic code
Back bone of DNA is a polymer

32. Natural Cycles
As living things grow die and decay, elements move between the spheres
Carbon cycle
Nitrogen cycle
Humans have an effect on these cycles

33. Human Effects Carbon Cycle: burning fossil fuels.
Raised CO2 from 277ppm to 360ppm
Nitrogen Cycle: Adding fertilisers to soil

34. Nitrogen Cycle Essential for biochemicals, especially proteins
N2 is a gas
NO3- (nitrate) and NH4+ (ammonium) are ions.
Attracted to water molecules so makes them dissolve

35. Fixing Nitrogen Action of micro organisms (bacteria or algae)
Chemical reaction in air during lightning strikes
Haber process

36. Metals from Lithosphere
Rocks which contain useful minerals are ores.
Valuable minerals are often oxides or sulphides of metals.
Ore examples: bauxite (aluminium), haematite (iron), rock salt (sodium).
Gold occurs naturally so has been used for thousands years. Couldn’t use other metals until learned how to extract.

37. Mineral Processing Valuable mineral mixed with dirt and rock
Separating this off is called ‘concentrating the ore.’
Issues: Reducing the ore; supply of ore; energy costs; impact on environment.

38. Extracting metals Reduction – removing oxygen (eg ZnO to Zn)
Reducing agent – something that removes oxygen (eg C)
In reducing something, the reducing agent itself becomes oxidised (CO)
Carbon is a good reducing agent as at high temperatures – it has a strong tendency to react with oxygen.

39. Relative atomic masses

40. Relative Formula Mass
If you know the formula of a compound, then you can work out its relative formula masses.
Eg Fe2O3
Fe – relative atomic mass = 56
O – relative atomic mass = 16
Therefore relative formula mass of Fe2O3 =
= 160

41. Atomic Mass Units
The actual mass of a hydrogen atom is 1.7x10-24g (that’s g!)
Far too small a number to easily get your head around…
So – we use Relative Atomic Masses.

42. Carbon is given a Ar of 12 (as it has 6 protons and 6 neutrons).
Relative Atomic Mass (Ar) tells us the mass of an atom compared to 1 atom of carbon.
Carbon is given a Ar of 12 (as it has 6 protons and 6 neutrons).
e.g. Ar of magnesium = Ar of fluorine = Ar of calcium =
Blah blah blah

43. We can use relative atomic masses to work out the relative formula mass (Mr) of a molecule or compound.
E.g. NaCl Ar of Na = 23 Ar of Cl = 35.5
So Mr of NaCl = = 58.5
E.g.2 H2O Ar of H = 1 Ar of O = 16
So Mr of H2O = (2 x 1) + 16 = 18

44. Calculate the relative formula mass of the following compounds (showing your working!):
(a) Carbon monoxide CO
(b) Carbon dioxide
(c) Sulphur dioxide SO2
(d) Calcium carbonate CaCO3
(e) Sodium hydroxide NaOH
(f) Sulphuric acid H2SO4
(g) Hydrochloric acid HCl
(h) Copper sulphate CuSO4
(i) Magnesium chloride MgCl2
(j) Sodium carbonate Na2CO3
(k) Lead nitrate Pb(NO3)2
(l) Calcium hydroxide Ca(OH)2

45. Electrolysis
Some reactive metals hold on to their oxygen too strongly so cannot use carbon as a reducing agent.
Use electrolysis
Aluminium extracted from bauxite.
Electrolysis turns ions back into atoms.

46. Electrolysis – What happens?
The electrolyte (liquid for electrolysis)
Aluminium forms at negative electrode because is attracted because positive.
Oxygen is negative so forms at the positive electrode.

47. Electrolysis-
Electrolysis turns ions back into atoms by giving them electrons.
Metal ions are positive so attracted to negative electrode
The flow of electrons from the power supply into the electrode is what makes it negative
In the electrolysis of molten aluminium oxide, the aluminium ions turn into aluminium atoms.

48. Electrolysis Al3+ + 3e- Al Aluminium electrons supplied Aluminium
ion by the negative
electrode

49. Electrolysis
Non-metal ions are negatively charged so attracted to positive electrode. Electrode is positive because electrons flow out of it to power supply.
Negative ions give up electrons to positive electrode and turn into atoms.
O O e-
ion atom electrons removed
by positive electrode

50. Metal Properties Strong Can be bent and pressed into shape
High melting points
Conduct electricity

51. Metallic Structures
Scientists imagine that the model for metallic structure uses:
Tiny spheres
Arranged in a regular pattern
Packed close together in a crystal as a giant structure.

52. Metallic bonding
Metals have a special kind of bonding – not ionic, covalent.
Metallic
Strong but flexible – allow to move atoms to new positions

53. Metallic Bonding
Metal ions tend to lose electrons in their outer shell easily.
In solid metal the atoms lose these electrons and become positive ions.
The electrons drift freely between the metal ions.
The attraction between them holds the structure together.

54. Metallic Bonding A metal crystal is not charged overall.
Total negative charge on electrons = total positive charge on ions.
Electrons can move freely between the ions – explains why metals conduct electricity well.

55. Life Cycle of Metals Mining – Large volumes waste rock
Large holes in ground
Explosives – noisy and produces dust
Open cast – large volumes red mud.

56. Life Cycle of Metals Processing Ores
Many ores high value but low grade
Large percentage waste rock

57. Life Cycle of Metals Metal Extraction
All stages of metal extraction and fabrication need energy
Use large volumes water
Give off air pollutants

58. Life Cycle of Metals Metals in Use
Lighter cars, trucks and trains mean less fuel consumption and emssions.
Less wear and tear on roads and tracks

59. Life Cycles of Metals Recycling
Scrap metal from all stages of production routinely recycled.
Metal recycled at the end of the usefulness of metal products.
Save ores and reducing agents. Save water.