Transcript module c5: chemicals of the natural environment

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.
Properties
Molecular
compounds
Ionic
compounds
Made from
Two or more non-metal
atoms bonded
Metal 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.
Mg 2+
O
Mg 2+ O 2- Mg 2+
Mg 2+
O 2- Mg 2+ O 2-
2-
O 2Mg 2+ O 2- Mg 2+
• The formula of magnesium oxide is
MgO
Na +
O
2-
O 2Na +
• The formula of sodium oxide is Na2O
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
1
2
3
4
5
6
7
0
ion
1+
2+
3+
None
321None
Lithosphere
• Made of the crust and
upper mantle
• Composed of minerals
e.g. quartz containing
silicon dioxide found in
granite and sandstone
Treasures of the Earth:
Gemstones for beauty, hardness, rarity
• Rich in the atoms of
silicon, oxygen and
aluminium
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
Biosphere
• the total sum of living organisms
• Contains large molecules such as
fats, carbohydrates, proteins, DNA
• Mostly: carbon, hydrogen, oxygen,
nitrogen
• Minor contributions from phosphorus
and sulphur
What’s the formula of the glucose
molecule above?
Cycling of
nutrients
•
Many elements
are cycled in
nature including
carbon, nitrogen
and oxygen.
•
Identify in the
cycle opposite
where carbon
can be found
as… (i) simple
molecular
compounds, (ii)
large molecules
and (iii) as the
element
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
lost oxygen
When oxygen is lost: REDUCTION
When oxygen is gained: OXIDATION
Overall the process is REDOX
+ carbon dioxide
gained oxygen
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
cathode
Al 3+
anode
O 2-
Al 3+
Al 3+
O 2-
O 2-
Molten
aluminium
metal drops
to the
bottom
oxygen
gas
released
• 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
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
Giant structure held together by ionic bonding
M+
M+
M+
M+
M+
M+
Metal ions in a lattice
Sea of electrons (free to move)
M+
M+
M+
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