Transcript AQA Chemistry Unit 1

AQA Chemistry Unit 1
Atoms
• All substances are made of atoms
• An element contains only one type of atom
• A compound contains more than one type of
atom chemically bonded together
• There are about 100 different elements in the
Periodic Table
The protons and neutrons exist
in a dense core at the centre of
the atom. This is called the
nucleus.
The electrons are spread
out around the edge of
the atom. They orbit the
nucleus in layers called
shells.
Particle
Mass
proton
neutron
1
1
electron
almost 0
Charge
+1
0
-1
Mass number:
the number of protons and
neutrons
Atomic number:
the number of protons
7
Li
3
So lithium has:
•3 protons
•7-3 = 4 neutrons
•3 electrons (atoms are neutral so always have the
same number of protons and electrons)
This electron arrangement is written as 2,8,8.
1st shell holds
a maximum of
2 electrons
2nd shell holds
a maximum of
8 electrons
3rd shell holds
a maximum of
8 electrons
The Periodic Table
• Columns are called GROUPS
• Elements in the same group have the same
number of electrons in their outer shell
• This gives them similar chemical properties
(think about the reactions of Group I metals in
water!)
• Group 0 – The Noble Gases – full outer shells
so are unreactive and do not form bonds.
Chemical Reactions
• Metal and a non-metal = IONIC BONDING
• Metal loses electrons and becomes a positive
ion
• Non-metal gains electrons and becomes a
negative ion
• Non-metals together = COVALENT BONDING
• Atoms share pairs of electrons to form
molecules
Word equations:
•Each reactant goes on the left separated by a ‘+’
•An arrow → represents them reacting together
•Each product goes on the right separated by a ‘+’
Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen
Symbol equations:
• There must be the same number of each atom on
both sides of the equation
• You can ONLY put big numbers in front of the
substances
Mg
+
HCl
→
MgCl2
+
H2
Conservation of Mass
• The mass of the products equals the mass of
the reactants
e.g. CaCO3
100g
→
→
?
CaO
+
+
44g
CO2
Limestone Cycle
This is the test
for CO2 gas!
Limestone
Bubble CO2 through
CaCO3
Calcium
Hydroxide
Solution
CO2 gas released
Calcium
Oxide
CaO
Ca(OH)2
Add more water
Thermal Decomposition
Calcium
Hydroxide
Ca(OH)2
Add water
This is an alkali and can
be used to neutralise
acids
Uses of Limestone
•
•
•
•
As a building material (buildings, statues etc)
Mortar – calcium hydroxide, sand and water
Cement – calcium oxide, clay and water
Concrete – cement and aggregate
Carbonates
• Other metal carbonates will thermally
decompose in a similar way to produce the metal
oxide and carbon dioxide
• Carbonates react with acids to produce a neutral
salt, water and carbon dioxide
calcium
carbonate
+
nitric → calcium + water + carbon
acid
nitrate
dioxide
Limestone buildings are damaged by acid rain because of this!
Metals
• An ORE contains enough metal to make it
economical to extract
• Unreactive metals like gold are found NATIVE
• Other metals are found as compounds (often
oxides) and require chemical reactions to extract
them
• Metals less reactive than carbon can be extracted
by REDUCTION with carbon
• Metals more reactive than carbon are extracted
using ELECTROLYSIS
The reactivity of a metal determines how it is extracted.
potassium
sodium
calcium
Metals above carbon in the reactivity
series must be extracted using
electrolysis. Electrolysis can also be used
to purify copper.
magnesium
increasing reactivity
aluminium
(carbon)
zinc
iron
Metals less reactive than carbon can be
extracted from their ores by reduction
using carbon, coke or charcoal.
lead
(hydrogen)
copper
silver
gold
platinum
Platinum, gold, silver and copper can
occur native and do not need to be
extracted.
Extraction
Reduction/smelting:
iron oxide + carbon → iron + carbon dioxide
2Fe2O3 +
3C → 4Fe +
3CO2
Electrolysis:
Aluminium must be molten
Large amounts of heat and electrical energy make
this very expensive
At the negative electrode:
Al3+ + 3e-  Al
(reduction)
At the positive electrode:
2O2-  O2 + 4e-
(oxidation)
aluminium oxide  aluminium + oxygen
2Al2O3 (l)
 4Al (l) + 3O2 (g)
Copper
• Purified by electrolysis
• Bioleaching uses bacteria to
separate copper from copper
sulphide – the leachate contains
copper which can be separated
by filtering
• Phytomining – plants grow in
soil containing copper. Plants
are burned and copper is
collected from the ash.
Impact of Extracting Metals
Quarrying
• Advantages:
— Useful products
— Money to local economy
— Local jobs
— Improved roads and transport
links
• Disadvantages:
— Scars landscape
— Noise and dust pollution
— Loss of habitats
Recycling
• Uses less energy and less
fossil fuels than extraction
• Conserves fossil fuels and
reduces CO2 emissions
• Saves money
• Conserves resources
• Reduces landfill
Properties of Metals
•
•
•
•
Strong
Malleable
Ductile
Good conductors of heat and electricity
• Different properties make metals useful for
different things
Alloys
• Mixture of metals
• Pure metals are often too soft – mixture
changes structure so layers can’t slide which
makes them stronger
• Iron from blast furnace is too brittle so…
Type of Steel
Properties
Uses
Low carbon steel (0.1% C)
Easily shaped
Car bodies
High carbon steel (1.5% C)
Very hard
Inflexible
Cutting blades
Bridges
Stainless steel (chromium
added)
Corrosion resistant
Cutlery
Containers for corrosive substances
Crude Oil
• Mixture of hydrocarbons (compounds
containing carbon and hydrogen ONLY)
• Most are ALKANES, CnH2n+2 (saturated)
•
•
•
•
Methane, CH4
Ethane, C2H6
Propane, C3H8
Butane, C4H10
Monkeys
Eat
Peeled
Bananas
Fractional Distillation
• The longer the carbon
chain the…
– Higher the bp
– Higher the viscosity
– Lower the flammability
Combustion of Fuels
Product
Problem?
Solution
Water
No
Carbon
dioxide
Yes – greenhouse gas,
contributes to global
warming
Use alternative fuels?
Carbon
monoxide
Yes - toxic
Catalytic converters
Sulphur
dioxide
Yes – causes acid rain
Sulphur impurities can be removed
before fuel is burned.
Gas scrubbers in power stations
Nitrogen
oxides
Yes – causes acid rain
Catalytic converters
Cracking
• Hydrocarbons can be cracked to make smaller, more useful
molecules
• This requires heat and a catalyst and is an example of thermal
decomposition
decane
(C10H22)

+
+
pentane
(C5H12)
propene
(C3H6)
ethene
(C2H4)
ALKENES
•
•
•
•
•
Alkenes contain a carbon-carbon double bond
CnH2n (unsaturated)
Ethene, C2H4
Propene, C3H8
To test for an alkene bromine water is added
and decolourises
Making Ethanol
Ethene from crude oil
• React with steam
• Catalyst
• Cheap
• Continuous process
• Produces 100% ethanol
• Non-renewable
• Requires high temp
Sugar cane
• Fermentation with yeast
• Renewable
• Lower temp
• Simpler equipment
• Requires land and can cause
food shortages in poorer
countries
• Only produces ~15% ethanol
• Batch process
Polymerisation
• Many alkene monomers react together to form a
polymer
• This requires pressure and a catalyst

monomers
addition polymerization
polymer
Repeating unit
Polymers
New developments
• New packaging materials
• Waterproof coatings for
fabrics
• Dental polymers
• Wound dressings
• Hydrogels
• Smart materials
Disposal
• Most are non-biodegradable
• Increases landfill and litter
• Reuse and recycling are
encouraged
• Biodegradable plastics made
from corn starch are being
developed
Plant Oils
• Can be extracted from fruits, seeds and nuts
Crush
Distil
Remove water
and impurities
• Vegetable oils have higher boiling points than water so food
can be cooked at higher temperatures
• Quicker
• Different flavours
• Increases energy the food releases (higher in fat!)
Fats
Saturated
• Higher boiling points (tend
to be solids at room temp)
• Unhealthy
Unsaturated
• Contain C=C – can be tested
for using bromine water
• Better for us
• Can be turned into
margarine by adding
hydrogen at 60oC with a
nickel catalyst
• This adds across some of
the double bonds and
increases the melting point
Emulsions
• Oil does not dissolve in
water
• It can form an emulsion
if an emulsifier is added
to stop it separating
• e.g. mayonnaise is a
mixture of oil and
vinegar with egg acting
as the emulsifier
emulsifier
water
oil
hydrophobic end
hydrophillic end
Earth’s Structure
Crust is split into tectonic plates
These move due to convection currents in the
mantle caused by heat released from radioactive
processes
Large movements can cause earthquakes and
volcanoes
Wegener’s Theory of Continental Drift
• Jigsaw like fit of continents
• Rocks containing similar fossils on Africa and
South America
• Others didn’t believe him  - they said there
could have been a land bridge and didn’t think
it was possible for the continents to move
• In the 1950’s new evidence was found that
proved him right! 
The Earth’s Atmosphere
about 21%
is oxygen
about 78%
is nitrogen
the remaining 1% is
mostly argon (0.93%)
with some carbon
dioxide (0.035%),
varying amounts of
water vapour and trace
amounts
of other gases
History
• First billion years – intense volcanic activity –
created the early atmosphere and oceans
• One theory – early atmosphere was mainly
carbon dioxide, water vapour and small
proportions of methane and ammonia.
• Miller-Urey is one theory for how life was
formed – hydrocarbons, ammonia and
lightning created amino acids.
Development
• Most of the carbon from the carbon dioxide in
the air became locked up in sedimentary rocks
as carbonates and fossil fuels
• Some dissolved in the oceans
• The level of carbon dioxide is increasing again
due to burning fossil fuels
Fractional Distillation of Air
•
•
•
•
•
Air is filtered to remove dust
Cooled to -200oC
Water vapour condenses and is removed
Carbon dioxide freezes and is removed
Liquified air is then heated slowly in the
column and the gases are separated