Atoms, Elements & Periodic Table
- Atoms have a small nucleus surrounded by electrons
- The nucleus is in the centre of the atom- it contains the protons and neutrons
- The whole mass of the atom is concentrated in the nucleus
- Electrons move around the nucleus shells
- Elements consist of one type of atom only
- Number of protons decides what type of atom it is
- Atoms can be represented by symbols
- The periodic table puts elements with similar properties together
- The vertical columns are called groups
- The horizantal rows are called periods
- If you know the properties of one elemnt, you can predict the properties of other metals in that group
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Compounds,Mixtures & Balancing Equations
- Atoms join together to make compounds
- Atoms form bonds with other atoms to form compounds
- Making bonds involves atoms giving away, taking or sharing electrons
- The properties of compounds are very different to those of the original elements
- Mixtures are easily separated- unlike compounds
- Air is a mixture of gases
- Crude oil is a mixture of different length hydrocarbon molecules
- A chemical reaction can be described by the process reactants --> products
- State symbols tell you what physical state somethings in:
- (s) solid (l) liquid (g) gas (aq) Dissolved in water
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- Limestone is used as a building material.
- Limestone is a grey/white colour- often formed from sea shells.
- It is quarried out of the ground
- St Pauls cathedral is made from limestone
- It is virtually insoluble in plain water, but acid rain reacts with it, causing erosion.
- It can be crushed up into chippings and used in road surfacing.
- Limestone is mainly calcium carbonate (CaCO3)
- When heated it thermally decomposes to make calcium oxide-CaO (quicklime) and carbon dioxide.Other carbonates decompose in the same way.
- Quicklime reacts with water to produce slaked lime- Ca (OH)2
- Slaked lime is actually calcium hydroxide. It is an alkali (can neutralise acid soils)
- Slaked lime works much faster than powdered limestone
- Limestone can also be used to make cement (heated in a kiln with powdered clay), then the cement can be mixed with sand & water to make mortar. It can also make glass.
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Using Limestone Advantages & Disadvantages
- Quarrying Limestone makes a right mess of the landscape.
- Blasting rocks apart causes noise pollution and also dust. Quarrying destroys habitats of animals and birds. The limestone needs to be transported away from the quarry - using lorries- causes more noise and air polluion. Waste materials produce unsightly tips.
- Making stuff from limestone causes pollution- cement factories make a lot dust (also cause breathing problems for some people). Energy is needed to produce cement and quicklime, the energy is most likely to come from burning fossil fuels- which causes more pollution.
- On the plus side- it provides houses and roads. Chemicals used in making dyes, paints and medicines also come from limestone. It can be used to neutralise acidic soils and acidity in lakes. It is used in power station chimneys to neutralise sulphur dioxide. It provides jobs for people.
- Limestone is widely available and it is cheaper than granite and marble. It looks attractive. etc.
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Properties of metals
- Metals are on the left and middle of the periodic table
- The transition metals are found in the centre block of the periodic table. Many of the metals in everyday use are transition metals- such as titanium, iron and nickel.
- Metals are strong and bendy and they're great conductors
- A metal's exact properties decide how its best used.
- Its the structure of the metals that gives them their properties.
- Metals consist of a giant structure of atoms held together with metallic bonds. These special bonds allow the outer elecron(s) of each atom to move freely.
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Metals from rocks
- Ores contain enough metals to make extraction worthwile.
- A type of iron ore is called haematite. This is iron (iii) oxide.
- The main aluminium ore is called bauxite. This is aluminium oxide.
- Copper ore is called chalcopyrite. This is copper iron sulphide.
- There's a limited amount of ores- they're finite resources.
- Copper is purified by Electrolysis.
- Copper is a transition metal. It is hard, strong and has a high melting point.
- Copper is a good conductor of electricity, so good for making wires.
- It can also be made into pipes, as it is below hydrogen in the reactivity series, it does not react with water. this makes it great for plumbing.
- Copper can be easily extracted by reduction with carbon; but the copper produced this way is impure- and impure copper doesn't conduct electricity very well.
- Electrolysis is used to purify it- even though it is quite expensive.
- Copper rich ores are in short supply- so it is important to recycle copper.
- Bacteria can be used to seperate copper from copper sulphide. The bacteria get energy from the bond between copper and sulphur, seperating out the copper in the process. this process is slow but environmentally friendly. Scientists are looking for new ways to extract copper from low grade ore or from the waste that is currently produced when copper is extracted.
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- More reactive metals are harder to get.
- A few unreactive metals like gold are found in the Earth as the metal itself, rather than as a compound.
- But most metals need to be extracted from their ores using a chemical reaction.
- More reactive metals, like sodium, are harder to extract- that's why it took longer to discover them.
- Some metals can be extracted by reduction with carbon.
- When an ore is reduced, oxygen is removed from it.
- The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon or carbon monoxide.
- Metals higher than carbon in the reactivity series have to be extracted by electrolysis, which is expensive.
- Metals below carbon in the reactivity series can be extracted by reduction using carbon. e.g. iron oxide is reduced in a blast furnace to make iron. This is because carbon can only take the oxygen away from metals which are less reactive than carbon itself is.
- A more reactive metal displaces a less reactive metal.
- More reactive metals react more strongly than less reactive metals.
- E.g. tin can be extracted from tin oxide by more reactive iron.
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Making metals more useful
- Pure iron tends to be too bendy
- iron straight from the blast furnace is only 96% iron. The other 4% is impurities such as carbon.
- Impure iron is brittle & is used for ornamental railings- but doesn't have many other uses.
- Pure iron has a regular arrangement of identical atoms. The layers of atoms can slide over each other, which makes the iron soft & easily shaped. This iron is far to bendy for most uses.
- Most iron is converted in steel- an Alloy.
- Steels are formed by adding small amounts of carbon and sometimes other metals to the iron.
- Low carbon steel (0.1% carbon)- easily shaped- car bodies
- High carbon steel (1.5% carbon)- very hard, inflexible- blades for cutting tools, bridges.
- Stain steel (chromium added, and sometimes nickel)- rust-resistant- cutlery, containers for corrosive substances.
- Alloys are harder than pure metals.
- Different elements have different sized atoms, sowhen carbon is added to pure iron, the smaller carbon atom will upset the layers of pure iron atoms, making it more difficult for them to slide over each other. So alloys are harder.
- BRONZE= COPPER + TIN
- CUPRONICKEL= COPPER + NICKEL
- gold alloys are used to make jewellery
- aluminium alloys are used to make aircraft.
- smart alloys return to their original shape
- They remember and return to their original shape when heated
- metal fatigue is a lot worse than in normal alloys
- smart alloys are also more expensive than steel or aluminium.
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More about metals
- Aluminium is useful but expensive to extract
- Aluminium has a low density and is corrosion- resistant
- Aluminium can be used for loads of things: window frames, electricity cables & aircraft.
- Aluminium has to be extracted by electrolysis. A high temp is needed to melt the oxide- this requires a lot of energy, which makes it an expensive process.
- ...and so is titanium
- Titanium is another low density metal, unlike aluminium it's very strong.
- It has a low chemical reactivity- which makes it corrosion resistant
- Titanium is used in spacecraft, jet engines and hip replacements
- Titanium needs lots of energy for extraction, like aluminium
- Metals can get tired when stresses and strains are repeatedly put on them over time. This is known as metal fatigue and leads to metals breaking, which can be very dangerous, eg in planes.
- Recycling metals is important
- Recycling metals only uses a fraction of the energy needed to mine and extract new metal. E.g. recycling copper only takes 15% of the energy that's needed to mine and extract new copper.
- Recycling saves money
- There's a finite amount of each metal in the Earth. Recycling conserves these resources.
- Recycling metals cuts down on the amount of rubbish that gets sent to landfill.
- Landfill takes up space & pollutes the surroundings. If all the aluminium cans in the uk were recycled, there'd be 14 million fewer dustbins each year.
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Fractional Distillation of Crude Oil
- Crude Oil is a mixture of different sized hydrocarbons
- Crude oil is formed from the buried remains of plants and animals- it's fossil fuel. Over millions of years, with a high temperature and pressure, the remains turn to crude oil which can be extracted by drilling and pumping.
- Hydrocarbons are basically fuels such as petrol and diesel. They're made of just carbon & hydrogen.
- Because it's a mixture the different hydrocarbon molecules aren't chemically bonded to one another- so they keep all their original properties, such as their condensing point.
- This means that crude oil can be split up into its seperate fractions by fractional distillation. Each fraction contains molecules with a similar length to each other.
- Crude Oil is split into seperate groups of hydrocarbons.
- The fractionating column works continuously, with heated crude oil piped at the bottom. The vaporised oil rises up the column and the various fractions are constantly tapped off at the different levels where they condense.
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Properties and Uses of Crude Oil
- The different fractions of crude oil have different properties, and it's all down to their structure.
- All the fractions of crude oil are hydrocarbons called alkanes.
- Alkanes are made up of chains of carbon atoms surrounded by hydrogen atoms.
- Different alkanes have chains of different lengths.
- The first four alkanes are methane (natural gas), ethane, propane and butane.
- Methane CH4- Ethane C2H6- Propane C3H8- Butane C4H10
- Carbon atoms form four bonds and hydrogen atoms only form one bond. Alkanes are saturated hydrocarbons. They contain as many hydrogen atoms as possible. All the bonds are single bonds (no double bonds).
- General Formula: CnH2n+2
- The longer the molecules, the less runny the hydrocarbon is- that is the more viscous it is.
- The shorter the molecules the more volatile they are- they turn into gas at a lower temperature.
- So, the shorter the molecules, the lower the temperature at which that fraction vaporises or condenses.
- The uses of hydrocarbons depend on their properties-
- The voltality helps decide what fraction it's used for. the refinery gas fraction has the shortest molecules- so it has the lowest boiling point- in fact its gas at room temp. this makes it ideal for use as bottled gas. It's stored under pressure as liquid in "bottles". When the tap on the bottle is opened, the fuel vaporises and flows to the burner where it's ignited.
- The viscosity also helps decide how the hydrocarbons are used. The really gloopy, viscous hydrocarbons are used for lubricating engine parts and for coverig roads.
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Using Crude Oil as a fuel
- Crude Oil provides an important fuel fo modern life.
- Crude Oil fractions burn cleanly so they make good fuels. Most modern transport is fuelled by crude oil fraction, e.g. cars, boats, trains and planes. Parts of crude oil are also burned in central heating systems in homes and in power stations to generate electricity.
- Crude oil provides the raw materials for making various chemicals, including plastics.
- Alternatives to using crude oil fractions as fuel are possible: e.g. electricity can be generated by nucleur power or wind power, there are ethanol-powered cars, and solar energy can be used to heat water.
- Crude oil fractions are often the easiest and cheapest thing to use.
- Crude oil fractions are often more reliable too- e.g. solar & wind power won't work without the right weather conditions. Nuclear energy is reliable, but there are lots of concerns about it's safety & the storage of radioactive waste.
- Most scientist think that oil will run out very soon.
- Crude oil is not the environments best friend- oils spills happen and can destroy animals habitat and kills fishes and birds. Also burning oil is thought to be the major cause of global warming, acid rain and global diming.
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- 90% of crude oil is used as fuel.
- Burning fuels releases gases and particles.
- When Fossil fuels are burnt, carbon dioxide and water vapour are always released into the atmosphere.
- hydrocarbon + oxygen --> carbon dioxide + water vapour
- Sulphur impurities are found in petrol and diesel so sulphur dioxide is also put in the air.
- If there is not enough enough oxygen for the fuel to burn properly, particles of soot (carbon) and carbon monoxide (a poisonous gas) are also released.
- Sulphur Dioxide causes acid rain.
- When the sulphur dioxide mixes with clouds it forms dilute sulphuric acid. This then falls as acid rain.
- Acid rain causes lakes to become acidic, causing many plants & animals to die as a result.
- Acid rain kills trees and damages limestone buildings and ruins stone statues.
- Sulphur can be removed from fuels before they are burnt, but it costs more. Also removing sulphur from fuels takes more energy. This usally comes from burning fuels, which release more co2. However petrol & diesel are starting to be replaced by low-sulphur versions.
- Acid rain is prevented by cleaning up emissions.
- Power stations now have Acid Gas Scrubbers to take the harmful gases out before they release their fumes into the atmosphere. Cars are now being fitted with catalytic converters to clean up their exhaust gases. The other way of reducing acid rain is simply to reduce our usage of fuels.
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Environmental Problems Cont.
- Increasing Carbon dioxide levels contribue to climate change.
- Most scientists believe this is the reason for average surface temp increasing.
- This warming could cause changes in climate and weather patterns all over the world. Flooding due to polar ice caps melting might happen too.
- Alternate fuels are being developed
- Ethanol- can be produced by fermentation of plants and is used to power cars in some places. It's often mixed with petrol to make a better fuel. Pros- the co2 released when it's burnt was taken in by the plant as it grew, so its a "carbon neutral." The only other product is water. Cons- Engines need to be converted before they'll work with ethanol fuels- and ethanol is widely available.
- Biogas- is a mixture of methane and co2. It's produced when microorganisms digest waste material. It can be produced on the large scale, or on the small scale where each family has it's own generator. Biogas is burned and the energy can be used for cooking, heating or lighting. Pros- waste material is readily available and cheap. it's a carbon neutral. Cons- biogas production is slow in cool weather.
- Hydrogen Gas- can also be used to power vehicles. You get the hydrogen from the electrolysis of water- there's plenty of water about but it takes electrical energy to split it up. This energy can come from a renewable source, e.g. solar. Pros- Hydrogen combines with oxygen in the air to form just water- so it's very clean. Cons- You need a special, expensive engine and hydrogen isn't widely available. You still need to use energy from another source to make it. Also, hydrogen's hard to store.
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Cracking Crude Oil
- Cracking means splitting up long-chain hydrocarbons.
- Long chain hydrocarbons form thick gloopy liquids like tar which aren't that useful.
- A lot of longer chain molecules produced from fractional distillation are turned into smaller ones by a process called cracking.
- Some of the products of cracking are useful fuels: e.g. petrol for cars & parrafin for jet fuel.
- Cracking also produces substances like ethene, which are needed for making plastics.
- Cracking is a thermal decomposition reaction- breaking molecule by heating them.
- The first step is to long-chain hydrocarbon to vaporise it (turn it ino a gas). Then the vapour is passed over a powdered catalyst at a temperature of about 400^0C- 700^0C. Aluminium oxide is the catalyst used. The long-chain molecules split apart or "crack" on the surface of the specks of catalyst.
- Most of the products of cracking are alkanes & alkanes.
- Kerosene (ten C atoms)--> Octane ( eight C atoms) + ethene
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Alkenes & Ethanol
- Alkenes have a C=C double bond.
- Alkenes are hydrocarbons which have a double bond between two of the carbon atoms in their chain.
- They are unsaturated because they can make more bonds- the double bond can open up, allowing the two carbon atoms to bond with other atoms.
- The first first three alkenes are ethene (2 Carbon atoms), Propene (3 Cs) & Butene ( four Cs).
- All alkenes have the formula CnH2n- they have twice as many hydrogens as carbons.
- Ethene- C2H4, Propene- C3H6, Butene- C4H8
- Ethene can be reacted with steam to produce ethanol.
- The reaction needs a temp of 300^0C and a pressure of 70 atmospheres. Phosphoric acid is used as a catalyst.
- This is a cheap process, but the problem is that ethene produced from crude oil is a non-renewable so it will start running out soon. This means it will become very expensive.
- Ethanol can also be produced from renewables.
- The alcohol & beer isn't made from ethene it's made by fermentation.
- The raw material for fermentation is sugar. This is converted into ethanol using yeast. This process needs a lower temperature (30-40^0C) & simpler equipment than when using ethene.
- another advantage is that raw materials are all renewable sources. Sugar is grown as a major crop in many parts of the world, yeast is also easy to grow.
- The ethanol produced this way can also be used as quite a cheap fuel in countries that don't have oil reserves to produce petrol.
- There are disadvantages though, The ethanol you get from this process isn't very concentrated, so it needs to be distilled to increase its strength. It also needs to be purified.
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Using Alkenes to make polymers
- Alkenes can be used to make polymers
- The most useful thing you can do with alkenes is polymeristaion. this means joining together lots of small alkene molecules- these long chain molecules are called polymers.
- E.g. Many ethene molecules can be joined up to produce poly(ethene) or "polythene".
- If you join lots of propene molecules together, you've got poly(propene)
- Different Polymers have different physical properties- and i depends on what it's made from.
- A polymers properties are affected by the temp & pressure of polymerisation. Poly (ethene) made at 200^0C & 2000 atmosphere pressure is flexible, and has low density. But poly (ethanol) made at 60^0C & a few atmospheres pressure with a catalyst is rigid & dense.
- And poly(ethenol) forms slime when it's mixed with different concentrations of sodium tetraborate. The more concentrated the sodium tetraborate, the more viscous and gungy the slime is.
- light, stretchable polymers e.g. low density poly(ethene)- plastic bags. Elastic polymer fibres- super stretchy spandex fibre for tights.
- new uses are developed all the time.- waterproof coatings for fabrics are made of polymers. Dental polymers (tooth fillings). Polymer hydrogel wound dressings keep wounds moist. Memory Foam is an example of a smart material. It's a polymer that gets softer as it gets warmer. Mattresses can be made of memory foam- they mould to your body shape when you lie on them.
- Polymers are cheap, but ost don't rot- they're hard to get rid of.
- Most polymers aren't biodegradable
- The best thing is to reuse them and recycle them.
- Things made from polymers are usually cheaper than things made from metals.
- However as crude oil gets used up, the prices will rise. Crude oil products like polymers will get dearer.
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Plant Oils & Emulsions
- we can extract oils from plants e.g. from fruits & seeds such as avacados & olives. Brazil nuts, peanuts and sesame seeds are oily seeds.
- These oils extracted can be used for food and for fuel.
- To get the oil out the plant material is crushed. The next step is to press the crushed plant material between metal plates and squash the oil out. This is the traditional method of producing olive oil.
- Oil can be seperated from crushed plant material by a centrifuge- rather like a spin dryer to get water out of wet clothes. or solvents can be used to get oil from plant material. Distillation refines oil and removes water, solvents and impurities.
- Vegetable oils are used in foods, they provide lots of energy and contain nutrients e.g. oils from seeds contain vitamin e. They also contain essential fatty acids which the body needs for many metabollic processes.
- Emulsions can be made from oil and water. Emulsions are made of lots of drops of one liquid suspended in another liquid. Emulsions are thicker than oil or water. e.g. mayonnaise is an emulsion of sunflower oil (or olive) and vinegar.
- The physical properties of emulsions make them suited to lots of uses- e.g. salad dressings and sauces. Generally the more oil you have in an oil and water emulsion, the thicker it is. Milk, single cream and double cream are all examples. Emulsions also have non-food uses- moisturising lotions.
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Using Plant Oils
- Unsaturated Oils contain C=C double bonds.
- Oils and fats contain long-chain molecules with lots of carbon atoms.
- Unsaturated oils contain double bonds between some of the carbon atoms in their carbon chains. C=C bonds can be detected by reacting with bromine or iodine. An unsaturated oil will decolourise bromine water or iodine water. Monounsaturated fats contain one C=C double bond somewhere in their carbon chains. Polyunsaturated fats contain more than one C=C bond.
- Unsaturated oils can be hydrogenated. They are liquid at room temp. They can be hardened by reacting them with hydrogen in the prescence of a nickel catalyst at about 60^0C. This is called hydrogenation. The hydrogen reacts with the double-bonded carbons and opens out double bonds.
- Hydrogenated oils often have a higher temp than unsaturated oils, so they're more solid at room temp. This makes them more useful as spreads and for baking cakes.
- Margerine is usually made from partially hydrogenated veg oil- to keep it nice, buttery and spreadable consistency. Partially hydrogenated oils are often used instead of butter in- biscuits. These oils are a lot cheaper than butter & they keep longer. Vegetable oils tend to be unsaturated while animal fats tend to be saturated.
- saturated fats are less healthier than unsaturated fats. saturated fats increase the amount of cholesterol in the blood. Natural unsaturated fats can reduce the amount of blood cholesterol such as olive & sunflower oil.
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- Processed foods often contain additives.
- E-numbers are additives that have passed safety tests in Europe.
- Artificial colours can be detected by chromotography.
- Preservatives- help food stay fresh.
- Colourings and Flavourings- make food look good and taste better.
- Emulsifiers & stabilisers stop emulsions spreading out.
- Sweetners- replace sugar in some foods- for diabetics.
- Some people are allergic to certain additives- e.g. the food dye tartrazine.
- Some additives aren't suitable for vegetarians- e.g. the food colouring cochineal comes from crushed insects. And gelatin from animal bones is used to thicken and set foods.
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- Wegeners theory of continental drift stated that there had been one supercontinent. thios land mass pangea, broke into smaller chunks which moved apart. He claimed that these chunks-our modern day continents- were slowly drifting apart.
- Wegeners theory wasn't accepted for many years as other scientists disagreed.
- It didn't help that he wasn't a proper geologist he had a phd in astronomy.
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The Earth's structure
- The earth has a crust, mantle, outer and inner core.
- The crust- is very thin (about 20km)
- The mantle has all the properties of a solid, except that it can flow very slowly. within the mantle-radioactive decay takes place-this produces a lot of heat- which causes the mantle to flow in convection currents.
- The centre of the earth is called the core- it is made of iron and nickel.
- The earth's surface is made of tectonic plates.
- The plates move a few centremetres a year
- Occasionally the plates move very suddenly causing an earthquake.
- Volcanoes often form at the boundaries between 2 tectonic plates.
- Scientists cant predict earthquakes and volcanic eruptions.
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The evolution of the atmosphere
- Phase 1- Volcanoes gave out gases- including co2, water vapour & nitrogen. We think this is how the oceans and atmosphere were formed. The oceans formed when the water vapour condensed.
- Phase 2-Green plants evolved & produced oxygen- the co2 dissolved into the oceans. the plants also removed co2 from the air and produced CO2. When the plants died and were buried under layers of sediment the carbon they had removed from the air as (co2) became locked up in sedimentary rocks as insoluble carbonates and fossil fuels. When we burn fossil fuels today, this locked up carbon is released and the concentration of CO2 in the atmosphere rises.
- Phase 3- Ozone layer allows evolution of complex animals. The build up of oxygen in the atmosphere killed of early organisms that couldnt tolerate it and more complex organisms began to evolve and flourish. The oxygen also created the ozone layer (o3) which blocked harmful rays from the sun and enabled even more complex organisms to evolve- us eventually.
- There is virtually no Co2 left now.
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The evolution of the atmosphere cont.
- about 1% of the atmosphere is noble gases.
- Noble gases are chemically unreactive. Argon is used in filament lamps- it's the atmosphere's most common noble gas. Neon is used in electric discharge tubes- when a current is passed through neon it gives out a bright light. helium is much less dense than air- it's used in party ballons and airships.
- There are competing theories about atmospheric change.
- The atmosphere is still changing- levels of co2 in the atmosphere are increasing
- Burning fossil fuels releases co2- and more and more fossil fuels are being burnt
- Deforestation also contributes to the increase, as there will be less plants to take in the co2
- The planet is getting hotter and co2 is a green house gas- which traps heat from the sun.
- The amount of ozone in the ozone layer has decreased. The ozone is broken down by man-made CFC's- widely used as aerosol propellants and fridge coolants. CFC's were phased out in 1900's.
- It's difficult to say whether changes in the ozone layer are to blame for skin cancer.
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