C5 Revision
Chemicals of the Natural
Environment
Objective
•To revise the whole
of C5
Three parts of the Earth
•Core
•Mantle
•Crust
The four spheres…
• Lithosphere: crust
and upper mantle
• Hydrosphere:
Oceans and rivers
• Atmosphere: Layer
of air around the
Earth
• Biosphere: sphere of
life
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
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
Bonds
• Small molecules
such as O2 or H2
do not split up
unless at
extremely high
temperatures
• Very strong bonds
between atoms
Different bonds
Single bonds
Double bonds
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
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.
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
Water molecules
• Three atoms appear at
an angle
• The hydrogen region
has a slight positive
charge
• The oxygen region
contains a slight
negative charge
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.
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.
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 nonmetal ions.
Lithosphere
• Top part of lithosphere is crust
• Rocks include boulders, stones and pebbles
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
Sandstone
• Made of mainly one
mineral
• Silicon dioxide
Limestone
• Made mainly of calcium
carbonate
Granite
• Mixture of quartz,
feldspar and mica
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.
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
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
Silica
•
•
•
•
Consists of silicon dioxide
Commonest form is quartz
One silicon to four oxygens
Form a 3D giant covalent
structure
Strong and rigid
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
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
Proteins
•
•
•
•
Hair skin and muscle.
Enzymes
Polymers made from amino acids
20 different amino acids
Proteins from amino acids
Carbohydrates
• Carbon
• Oxygen
• Hydrogen
Sugars such as glucose
Photosynthesis produces glucose
Glucose very soluble
Nucleic Acids
• DNA and RNA are nucleic acids
• Molecules that carry the genetic code
• Back bone of DNA is a polymer
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
Human Effects
• Carbon Cycle: burning
fossil fuels.
• Raised CO2 from
277ppm to 360ppm
• Nitrogen Cycle: Adding
fertilisers to soil
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
Fixing Nitrogen
• Action of micro organisms (bacteria or algae)
• Chemical reaction in air during lightning
strikes
• Haber process
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.
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.
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.
Relative atomic masses
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 =
• 56+56+16+16+16 = 160
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.
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.
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.
Electrolysis
• Al3+
+
3eAluminium
electrons supplied
ion
by the negative
electrode
Al
Aluminium
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.
• O2O
+
2eion
atom
electrons removed
by positive electrode
Metal Properties
•
•
•
•
Strong
Can be bent and pressed into shape
High melting points
Conduct electricity
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.
Metallic bonding
• Metals have a special
kind of bonding – not
ionic, covalent.
• Metallic
• Strong but flexible –
allow to move atoms to
new positions
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.
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.
Life Cycle of Metals
• Mining – Large volumes
waste rock
• Large holes in ground
• Explosives – noisy and
produces dust
• Open cast – large
volumes red mud.
Life Cycle of Metals
• Processing Ores
• Many ores high value
but low grade
• Large percentage waste
rock
Life Cycle of Metals
• Metal Extraction
• All stages of metal
extraction and
fabrication need energy
• Use large volumes
water
• Give off air pollutants
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
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.