Chemistry Unit 1

• Atoms have a small nucleus surrounded by electrons 
• The nucleus contains protons and neutrons 
• The nucleus is tiny compaired to the rest of the atom 

Charges:

• Protons - positively charged 
• Neutrons - no charge 
• Electrons - negatively charged 

- Number of protons equals the number of electrons 

- Atoms have no overall charge 

Elements consist of one type of atom only 

• Atoms can be represented by symbols 
• The periodic table puts atoms with similar properties together 
• Vertical columns are called groups 
• All the elements in a group have the same amount of electrons in their outer shell 

Elements in the same group have similar properties 

Electron shell rules:

• Electrons always occupy shells (sometimes called energy levels)
• The lowest energy levels are always filled first (ones closest to the nucleus)
• Only a certain number of electrons are allowed in each shell (1st - 2, 2nd - 8, 3rd - 8)
• Atoms are much 'happier' when they have full electron shells like noble gases (group 0/8)
• In most atoms the outer shell isn't full, making the atom want to react to fill the outer shell

Atoms join together to make compounds:

• Different elements react to form chemical bonds with each other called compounds
• Compounds are usually difficult to seperate out 
• Making bonds involves atoms giving away, taking or sharing electrons (only electrons are involved)
• When a metal and non-metal form a bond it is called ionic bonding (the metal atoms lose electrons and the non-metal atoms gain electrons)
• When non-metals form a bond it is called covalent bonding (they share electrons)
• Properties of compounds are totally different to the properties of the original elements 

A formula shows what atoms are in a compound 

• Atoms aren't lost or made in chemical reactions 
• Balance just one type of atom at a time 
• You need the same amount of each atom on both sides of the equation 

Limestone is mainly calcium carbonate:

• It is quarried out of the ground 
• When heated it thermally decomposes to produce calcium oxide and carbon dixoide
• It also reacts with acid to produce a calcium salt, carbon dioxide and water 
• Calcium oxide reacts with water to produce calcium hydroxide 
• Calcium hydroxide is an alkali that can be used to neutralise acidic soil in fields 
• Calcium hydroxide reacts with carbon dioxide to produce calcium carbonate and water 

Useful things limestone makes:

• Powdered limestone heated with powdered clay makes cement 
• Cement mixed with sand and water produces mortar 
• Cement mixed with sand and aggregate produces concrete 

Quarring limestone:

• Makes huge ugly holes that permanently change the landscape 
• Makes lots of noise and dust 
• Destroys habitats of plants and animals 
• Lorries to transport away the limestone cause noise and pollution 
• Waste materials produce unsightly tips 
• Cement factories make lots of dust (breathing problems)
• Energy is needed to produce cement and stuff (from burining fossil fuels (pollution))

Advantages:

• Provides things people want (e.g houses and roads)
• Chemicals to make things like dyes, paints, medicine ect come from limestone 
• Can be used to neutralise acidic soils and water in lakes 
• Used in power station chimneys to neutralise sulfur dioxide 
• Provides jobs for people and brings money into the local economy leading to local improvements 
• Landscaping and restoration normally occurs after quarring is over as part of regulations 

Limestone products have advantages and disadvantages: 

• Limestone is widely available and cheaper than granite or marble 
• It is an easy rock to cut 
• Some is more hard-wearing than marble but still looks attractive 
• Concrete can be moulded 
• Quick and cheap way of constructing buildings (concrete... and it shows)
• Don't rot when they get wet 
• Can't be gnawed by insects or rodents 
• Fire resistant 
• Doesn't corrode 

- Ores contain enough metal to make extraction worthwhile 

Methods metals are extracted:

• Reduction by carbon 
• Electrolysis (also used for purification of metals)

Reduction (with carbon):

• Metals lower than carbon in the reactivity series follow this method 
• When an ore is reduced, the oxygen is removed from it 
• Metals below carbon that can be extracted by this method are; zinc, iron, tin and copper 

Electrolysis:

• Breaking down of a substance using electricity 
• Requires a liquid to conduct the electricity (electrolyte)
• Often metal salt solutions or molten metal oxides 
• Electrolyte has free ions that conduct the electricity 
• Electrons are taken at the positive anode and given at the negative cathode 

Purification of copper by electrolysis:

• The copper produced from reduction is impure and doesn't conduct electricity 
• This isn't useful as lots of copper is used for electrical wiring 
• Electrolysis is therefore used to purify it (although it is quite expensive)

Extracting copper using displacement: 

• Putting a more reactive metal than copper (scrap iron which is cheap unlike copper) in a solution of dissolved metal compound causes the more reactive metal to replace the less reactive metal in the compound 
• More reactive metals bond more strongly so it pushes out the less reaaactive metal 

Bioleaching - uses bacteria to seperate copper from copper sulfide, bacteria get energy from the bond between the atoms which seperates copper out from the ore in the process. The leachate (solution formed) can then be filtered to extract the copper. 

Phytomining - plants are grown in soil containing copper, they can't use or get rid of the copper so it builds up in their leaves. The plants are then harvested, dried and burnt in furnaces. The copper can then be collected from the ash left in the furnace. 

Pros - useful products made, provides jobs to locals and brings money into an area which can then help improve the area. 

Cons - causes noise, pollution, landscape scarring and habitat loss. Deep mine shafts can also be dangerous for a long time after they are abandoned. 

Importance of recycling metals:

• it takes lots of energy to mine and extract metals (comes from burning fossil fuels)
• fossil fuels are running out so need conserving 
• burning them contributes to acid rain, global warming and global dimming 
• recycling metals only uses a small fraction of the energy that it would take to mine and extract more 
• energy isn't cheap so recycling also saves money 
• there is a finite amount of metal on earth so recycling conserves the resources 
• it cuts down on landfill space that is used 
• landfill takes up space and pollutes the surroundings 

Basic properties:

• They are strong but can be bent or hammered into different shapes
• They are good heat conductors 
• They are good electrical conductors 

Copper - good electrical conductor, hard and strong but can be bent and doesn't react with water so is good for electric wiring and things like pipes for plumbing 

Aluminium - corrosion resistant, low density, strong as an alloy and can be bent in to shape, also light so would be good for making aeroplanes 

Titanium - low density, very strong, corrosion resistant and light so is good for things like replacement hips 

Metals aren't perfect...

• some corrode in water and air so need painting to protect them 
• metal fatigue can occur from repeated strains and stresses which leads to the metal breaking 

Pure iron tends to be too bendy:

• iron straight from the furnace is only 96% iron as the other 4% is impurities like carbon 
• impure iron is used as cast iron for making ornamental railings but doesn't have other uses as it is too brittle 
• all impurities are therefore removed to leave iron with a regular atom arrangement 
• this makes iron soft and easily shaped which means it is too bendy 

Most iron is converted into steel (an alloy):

• Low carbon steel (0.1% carbon) - easily shaped so used for car bodies 
• High carbon steel (1.5% carbon) - very hard and inflexible so used for bridges and cutting tool blades 
• Stainless steel (chromium and nickel added) - corrosion-resistant so used for cutlery and corrosive substance containers 

Alloys are harder than pure metals: 

• bronze = copper + tin 
• bronze is harder than copper and good for things like medals and statues 
• cupronickel = copper + nickel 
• cupronickel is hard and corrosion resistant so is good for making 'silver' coins 
• gold alloys are used to make jewellery as pure gold is too soft so metals such as zinc, copper, silver, palladium and nickel are used to harden it 
• aluminium alloys are used to make aeroplanes 

• crude oil is a mixture of hydrocarbons 
• they aren't chemically bonded together 
• the different length hydrocarbons keep their original properties (e.g condensing point)

The process: 

• the crude oil is vaporised and pumped in at the bottom of the column 
• it is hotter at the bottom and cooler at the top 
• the vapor rises up the column and when each molecule length reaches its condesning point it condenses and is tapped off at that fraction 
• gases come out  the top and more viscous liquids come out the bottom 
• the higher you go up the shorter the molecule length is (longer ones are nearer the bottom)

• crude oil is alkanes 
• alkanes are saturated and have single carbon to carbon bonds in them 
• the general formula for them is: 

Basic trends:

• the shorter the molecule the more runny (less viscous)
• the shorter the molecule the more volatile (lower boiling point)
• the shorter the molecule the more flammable 

Uses depend on properties:

• shorter molecules are good for bottled gas as they can be a liquid under pressure and once released from the bottle they will be a gas 
• longer molecules (liquids) are good as fuels like petrol as it can flow to the engine to be vaporised and mixed with air to be ignited 
• really long chain molecules are viscous so are good for things like tarmac and lubricatng parts 

Positives:

• burns cleanly so good for transport fuels but also for central heating systems and power stations 
• there is a massive industry for obtaining crude oil 
• provides raw materials for chemicals including plastics 
• things tend to be set up for using crude oil (e.g engines)
• crude oil fractions tend to be easiest and cheapest 
• crude oil fractions tend to be more reliable too as don't rely on conditions 

Negatives:

• it will run out one day as it is a non-renweable fuel 
• it will take time to develop alternative fuels 
• it will take time to adapt things like engines 
• oil spills can happen which poisons and kills animals and plants 
• burning the oil releases green house gases and particulates which causes global warming, acid rain and global dimming 

Acid rain :

• caused by sulfur dioxide mixing with clouds (water vapour) to produce dilute sulfuric acid 
• nitrogen oxides also react in the same way to form dilute nitric acid 
• this acid then comes down as rain which causes lakes to become acidic and many animals and plants to die as a result 
• acid rain also kills trees, damages limestone buildings and ruins limestone statues 

Reducing sulfur emissions:

• most sulfur can be removed from fuels before they are burnt but it costs more 
• removing sulfur from fuels also uses more energy which usually comes from burning more fuel that will realease carbon dioxide which causes global warming 
• power stations now have acid gas scrubbers that take the harmful gases out before they release their fumes into the atmosphere 
• the other way to reduce it is to reduce our usage of fossil fuels 

Carbon dioxide increase causes climate change- this can change rainfall patterns, cause ice caps to melt and can cause severe flooding and species to become extinct, it also makes the sea more acidic

Particles cause global dimming - particles of carbon from incomplete combustion are reflecting sunlight back into space which has reduced the amount of light we recieve 

Alternative fuels :

• Ethanol - produced from plant material so is called a biofuel. It is carbon neutral and the only other thing released is water but engines would need converting, ethanol isn't widely available and due to farmers switching to making ethanol so food prices would go up.
• Biodiesel - produced from vegetable oils and can be mixed with diesel to run in an ordinary diesel engine. It is carbon neutral, engines don't need converting and it produces less sulfur dioxide and particulates than normal diesel would.
• Hydrogen gas - obtained from the electrolysis of water which takes up energy but could come from a renewable resource. It combines with air to form water so is very clean but you would need a special, expensive engine, you would need energy from another source to make it and it is hard to store. 

Cracking means spliiting up long chain hydrocarbons:

• it splits up long chain hydocarbons that aren't very useful into smaller and more useful ones 
• it is a thermal decomposition reaction as breaks molecules down by heating them 

The process:

• vaporise the long chain hydrocarbons 
• pass the vapour over a powdered catalyst (aluminium oxide) at a temperature of about 400 - 700 degrees celcius 
• the long chain molecules split apart/crack on the surface of the catalyst specks 
• the products tend to be alkanes and some alkenes 

An alternatice way of cracking them is to mix the vapour with steam at a very high temperature 

Alkenes:

• have a carbon to carbon double bond 
• unsaturated as they can make more bonds 
• have the general formula: 
• the test for an alkene is bromine water as an alkene with make it go colourless because the double bond will open up to form a bond with the bromine

 Steam hydration of ethene:

• ethene can be hydrated with steam in the prescence of a catalyst to make ethanol 
• this is a cheap process and not much is wasted 
• ethene is produced from crude oil which will run out so it will become expensive 

Fermentation of sugar with yeast:

• sugar and yeast gives carbon dioxide and ethanol 
• it needs a lower temperature and simpler equipment than using ethene 
• sugar is a renewable resource 
• it is quite a cheap fuel too 
• the ethanol you get isn't very concentrated so to increase it's strength it has to be distilled 
• it also needs to be purified 

Polymerisation: 

• the joning together of many alkene monomers to produce large chain polymers 
• it is done under extreme pressure and in the prescence of a catalyst 

Different polymers have different properties:

• higher temperatures and pressures cause the polymer to be flexible and low density 
• lower temperatures and pressures with a catalyst cause the polymer to be rigid and dense 

Uses include: plastic bags, lycra for tights, waterproof coatings for fabrics, dental polymers for tooth fillings, hydrogel wound dressings to keep the wound moist, memory foam (a smart material) and biodegradable packagings can be made with polymers and corn starch 

• most polymers aren't biodegradable 
• reusing them is best as otherwise they take up space in landfill 
• polymers are usually quite cheap  but the prices will rise as crude oil gets used up 

Extracting plant oils:

• plant material is crushed adn then pressed between metal plates to squeeze out the oil 
• oil can be seperated from a crushed plants using a centrifuge 
• solvents can be used to get oil from plant material 
• distillation refines oil as it removes any water, solvents and impurities 

Vegetable oils in food:

• provide a lot of energy, contain nutrients and essential fatty acids 
• they have higher boiling points so can cook food faster and at a higher temperature 
• they give food a different flavour (oil carries the flavour making it seem more intense)
• increases the energy we get from food when they are cooked in it 

Vegetable oils can be used to produce fuels:

• suitable as fuels as they provide lots of energy 
• biodiesel is a useful fuel from vegetable oils 

Unsaturated oils:

• contain carbon to carbon double bonds so will decolourise bromine water 
• monounsaturated fats contain one carbon to carbon doubled bond and polyunsaturated fats contain more than one carbon to carbon double bond 

Hydrogenation: 

• unsaturated fats are liquid at room temperature but can be hardened by reacting them with hydrogen in the prescence of a nickel catalyst at 60 degrees celcius 
• the hydrogen reacts with the double bonds and opens them out 
• hydrogenated oils are useful as spreads for baking cakes and pastries, they are only partially hydrogenated as if they were hydrogenated fully they would be too hard to spread 
• they are cheaper and keep longer than butter but you also end up with a lot of trans fats that are suggested to be bad for you 

Health problems - saturated fats are less healthy than unsaturated fats as they increase blood cholesterol levels which can block arteries and increase the risk of heart attacks. Cooking with oil makes food more fattening. animal fats tend to be saturated and vegetable oils unsaturated

Emulsions:

• oils don't dissolve in water but you can mix them to make an emulsion 
• emulsions are made up of lots of droplets suspended in another liquid 
• emulsions are thicker than oil or water (e.g mayonaise)
• the physical properties are good for things like salad dressings as you get a better coverage 
• generally the more oil, the thicker the emusion (hence why cream is thicker than milk)
• whipped cream and ice cream also have air mixed into them to make them more fluffy 
• emulsions also have uses in paints and moisturising lotions ect

Emulsifiers:

• have a hydrophilic head (attracted to water) and hydrophobic tail (attracted to oil)
• cause the emulsion to not seperate out 
• emulsifiers stop emulsions seperating out and increase shelf life 
• allow food companies to produce foods lower in fat but still with a good texture 
• some people are allergic to them which is bad 

Wegeners theory of continental drift:

• came across very similar fossils of plants and animals on opposite sides of the atlantic ocean 
• he investigated further and found other similar cases of very alike fossils very far away 
• others just accepted the explanation there had once been land bridges linking continents so animals could cross but they had since sunk 
• he also noticed the coastlines of South America and Africa seemed to match up like a jigsaw puzzle so he wondered if they had once been together bun since split 
• there were matching layers of rocks in the continents and fossils had been found in the 'wrong' places (e.g the present climate would have killed them off)
• he proposed there had once been a 'supercontinent' that has since broken up and drifted apart 

Wasn't accepted because...

• his explanation for the drifting wasn't very convincing as he thought continents were ploghing through the sea beds and the movement was caused by tidal forces and the earth's rotation which other geologist's said was impossible due to calculations proving it wouldn't work 
• although he was wrong he did have the main idea correct 

• crust (very thin)
• mantle (convection currents within  due to radioactive decay creating heat)
• outer and inner core (made of iron and nickel)

Earth's surface:

• crust and upper part of the mantle are cracked into large pieces called tectonic plates
• convection currents in the mantle cause them to drift 
• most move by a few cm's a year 
• occasionally they move suddenly causing an earthquake
• volcanos and earthquakes occur at plate boundaries 

earthquakes can't really be predicted and even volcanos can be tricky to predict at times 

Atmosphere now - 78% nitrogen, 21% oxygen and small amounts of other gases 

Phase 1 - Volcanoes gave out gases

• originally the surface was molten so any atmosphere would have 'boiled away' into space 
• things cooled down and a thin crust formed but volcanos kept erupting 
• the volcanos gave out lots of gas which formed the oceans and atmosphere
• early atmoshpere was probably mostly carbon dioxide and virtually no oxygen. There may also have been water vapour, and small amounts of methane and ammonia. 
• the oceans formed when the water vapour condensed 

Phase 2 - Green plants evolved and produced oxygen 

• green plants and algae evolved and they used the carbon dioxide in photosynthesis and produced oxygen 

Phase 3 - Ozone layer allows evolution of complex animals

• oxygen created the ozone layer and allowed more complex organisms to evolve, there is virtually no carbon dioxide left in the atmosphere now 

Miller and Urey - Primordial soup: 

• atmosphere was nitrogen, hydrogen, ammonia and methane and lightning struck causing chemical reactions between the gases resulting in the formation of amino acids
• these collected in a 'primordial soup' a body of water out of which life gradually crawled as the amino acids combined to produce organic matter that eventally evolved into living organisms 
• in the 1950's Miller and Urey carried out an experiment to prove this theory, sealing the gases in their apparatus, heated it and applied an electrical charge for a week
• they found that amino acids were made suggesting the theory could be on the right lines 

Fractional distillation of air:

• air is filtered to remove dust 
• it is then cooled to -200 degrees and becomes a liquid 
• during cooling water vapour condenses and is removed 
• carbon dioxide freezes and is removed 
• the liquified air enters the fractionating column and is heated slowly 
• the remaining gases are filtered by fractional distillation, oxygen and argon come out together so another column is used to seperate them