AQA Chemistry Unit 1. Atoms All substances are made of atoms An element contains only one type of...
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Transcript of AQA Chemistry Unit 1. Atoms All substances are made of atoms An element contains only one type of...
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 electrons are spread out around the edge of the atom. They orbit the nucleus in layers called shells.
The protons and neutrons exist in a dense core at the centre of the atom. This is called the nucleus.
-1almost 0electron
01neutron+11proton
ChargeMassParticle
7
Li3
Mass number:the number of protons and neutrons
Atomic number:the number of protons
So lithium has:
•3 protons
•7-3 = 4 neutrons
•3 electrons (atoms are neutral so always have the same number of protons and electrons)
1st shell holdsa maximum of2 electrons
2nd shell holdsa maximum of8 electrons
3rd shell holdsa maximum of8 electrons
This electron arrangement is written as 2,8,8.
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 ‘+’
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
Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen
Mg + HCl → MgCl2 + H2
Conservation of Mass
• The mass of the products equals the mass of the reactants
e.g. CaCO3 → CaO + CO2
100g → ? + 44g
Limestone Cycle
Thermal Decomposition
CO2 gas released
Add waterAdd more water
Bubble CO2 through
This is the test for CO2 gas!
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 + nitric → calcium + water + carboncarbonate 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
potassium
sodium
calcium
magnesium
aluminium
zinc
iron
copper
gold
incr
easi
ng re
activ
ity
Metals above carbon in the reactivity series must be extracted using electrolysis. Electrolysis can also be used to purify copper.
Metals less reactive than carbon can be extracted from their ores by reduction using carbon, coke or charcoal.
Platinum, gold, silver and copper can occur native and do not need to be extracted.
lead
silver
The reactivity of a metal determines how it is extracted.
(carbon)
(hydrogen)
platinum
Extraction
Reduction/smelting:iron oxide + carbon → iron + carbon dioxide 2Fe2O3 + 3C → 4Fe + 3CO2
Electrolysis:Aluminium must be moltenLarge amounts of heat and electrical energy make this very expensive
At the negative electrode:
Al3+ + 3e- Al (reduction)
aluminium oxide aluminium + oxygen 2 Al2O3 (l) 4 Al (l) + 3 O2 (g)
At the positive electrode:
2O2- O2 + 4e- (oxidation)
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 hardInflexible
Cutting bladesBridges
Stainless steel (chromium added)
Corrosion resistant CutleryContainers for corrosive substances
Crude Oil
• Mixture of hydrocarbons (compounds containing carbon and hydrogen ONLY)
• Most are ALKANES, CnH2n+2 (saturated)
• Methane, CH4 Monkeys
• Ethane, C2H6 Eat
• Propane, C3H8 Peeled
• Butane, C4H10 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
addition polymerizationmonomers
polymer
Repeating unit
PolymersNew 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
• 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
water
oil
emulsifier
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 78% is nitrogen
about 21% is oxygen
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