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