GCSE core chemistry revision 1

FUNDAMENTAL IDEASATOMS, ELEMENTS AND COMPOUNDS all substances made up of atoms- substances made up of only one type of atom = elements symbols for elements are universal- put on a periodic table elements arranged in the periodic table down columns called groups. Each group contains elements with similar chemical properties different types of atom chemically bonded together = compounds An atom is made up of a tiny central nucleus with electrons around it ATOMIC STRUCTURE nucleus contains protons and neutrons- particles orbiting are electrons atom, same no. of protons and electrons, no overall charge number of protons = atomic number, elements arranges in their atomic number no. of protons and neutrons = mass number no. of neutrons= mass number - atomic number ARRANGEMENT OF ELECTRONS IN ATOMS around the nucleus in shells- each shell represents a different energy level. Lowest energy level is the shell nearest the nucleus. Electrons in an atom occupy the lowest available energy level. elements in the same group have the same number of electrons in their outer shell (group 1= 1 electron = alkali metals) chemical properties of an element depend on how many electrons it has, the way an element reacts depends o its no. of electrons in its outer shell ( so elements in a group react similarly) group 0 = noble gases- unreactive (all have full outer shells) FORMING BONDS some atoms react by transferring electrons (ionic, metals and non-metals) or sharing electrons (covalent, non-metal and non-metal) ionic- atoms become charged particles (ions) (metal become positive, non-metal become negative)- ionic bonds are the opposite attractions between the positive and negative ions compounds have no overall charge covalent bonding, electrons shared, covalent overlapping bonds CHEMICAL EQUATIONS using symbol equations helps us to see how much of each substance is reacting, more useful than word equations because word equations only useful if everyone who reads them speaks the same language, word equations don't tell us how much of each substance is involved and word equations can get very complicated when lots of chemicals are involved. the total mass of the products formed in a reaction is equal to the total mass of the reactants- equations are balanced, same no of each type of atom on both sides of the equation

ROCKS AND BUILDING MATERIALSLIMESTONE AND ITS USES made mainly of calcium carbonate- some types of limestone were formed from the remains of tiny animals and plants that lived in the sea millions of years ago- dig limestone out of the ground in quarries  USES- building material, powdered limestone can be heated with powdered clay to make cement and then concrete (cement powder mixed with water, sand and crushed rock) chemical formula = CaCO3  when we heat limestone strongly, it breaks down to form calcium oxide ( and carbon dioxide) = thermal decomposition chalk is a form of limestone calcium oxide is a useful substance in the building and farming industries  a rotary lime kiln- furnace that makes calcium oxide- fill the kiln with crushed limestone and heat strongly using a supply  of hot air. Calcium oxide comes out of the bottom and waste gases (CO2) leave the kiln at the top. Kiln rotates so the limestone is thoroughly mixed with the stream of hot air. (completely decomposes) REACTIONS OF CARBONATES Calcium carbonate reacts with acid, so acid rain corrodes buildings made of limestone CO2 turns limewater cloudy (limewater is alkaline, CO2 is weakly acidic so reacts with it producing tiny solid particles of insoluble calcium carbonate as a precipitate, precipitate makes the limewater turn cloudy)  carbonates react with acids to give a salt, water and carbon dioxide many metal carbonates decompose when heated in a Bunsen flame, they form the metal oxide and carbon dioxide THE LIMESTONE REACTION CYCLE Add water to calcium oxide to produce calcium hydroxide- reaction gives out a lot of heat, dissolve a little calcium hydroxide in water and after filtering produces limewater add CO2 to limewater- makes calcium carbonate CaO+H2O-Ca(OH)2--- Ca(OH)2+CO2-CaCO3+H20-- CaCO3-CaO+CO2 calcium hydroxide is an alkali- reacts with acids in a neutralisation reaction- products are a salt and water. Calcium hydroxide is used by farmers to improve soil that is acidic (neutralises it)- also used to neutralise acidic waste gases in industry before releasing gases into the air CEMENT AND CONCRETE mortar= calcium hydroxide mixed with sand & water mortar holds other building materials together (reacts with CO2 in the air producing limestone so effectively held together by rock) the amount of sand in the mixture is important- modern mortars now use cement instead of calcium hydroxide lime mortar doesn't harden very quickly and won't set at all where water prevents it from reacting with CO2 heating limestone with clay in a kiln produces cement the mortar used to build a modern house is made by mixing Portland cement and sand, sets when mixed thoroughly with water and left for a few days concrete- add aggregate to water, cement and sand LIMESTONE ISSUES Mining limestone (useful raw material) affects the local community and environment a quarry forms a huge hole in the ground, blasting and exploding the limestone from the rock face scars the landscape and scares off wildlife and disturbs local residents huge crater formed can be filled with water and used as a reservoir or for leisure activities. Also possibility to use as landfill sisters for household rubbish before covering with soil and replanting offers employment and aids local businesses DEVELOPMENTS IN LIMESTONE, CEMENT AND CONCRETE- before cement mortar was invented, lime mortar was used however this takes much longer to set, especially in wet conditions- carbon dioxide is produced in burning fossil fuels to heat kilns and in the reaction itself (during manufacture of cement), using lime mortar would use less CO2 as it absorbs CO2 as it sets- concrete is reinforced using glass and carbon fibres or steel rods, some of the latest research uses recycled paper to improve concrete's resistance to cracking, impact and scratching, reinforcing materials are shredded before adding them to the concrete mixture-reinforced concrete is cheaper than iron or steel but steel is harder. A Bunsen burner flame can't get hot enough to decompose sodium carbonate or potassium carbonate

METALS AND THEIR USESEXTRACTING METALS metals are found in the earth's crust- find most metals combined chemically with other chemical elements (oxygen), so must be chemically separated from its compounds before use where there is enough of a metal compound or metal in a rock to make it worth extraction, the rock is a metal ore ores are mined from the ground and some need to be concentrated before the metal is extracted and purified (copper ores are ground into powder), they are then mixed with water and a chemical that makes the copper compound repel water, air is then bubbled through the mixture and the copper compound floats on top as a froth (rocky bits sink), then scraped off the top ready for copper extraction whether it is worth extracting a metal depends on how easy it is to extract it from its ore and how much metal the ore contains, these 2 factors change over time- an ore that was once thought of as low grade could become and economic source of a metal due to new cheaper methods being discovered some metals are so unreactive that they are found in the Earth as the metals themselves (gold and silver). Occur in a native state. gold flakes can be physically separated from sand and rocks by panning the way we extract a metal depends on its place in the reactivity series- a more reactive metal will displace a less reactive metal from its compounds, carbon (a non-metal) will also displace less reactive metals from their oxides (this is used in industry)  find many metals combined with oxygen- metal oxides. carbon is more reactive than copper, lead, iron and zinc so can be used to extract the metals from their oxides- heat the metal oxide with carbon, carbon removes oxygen to form CO2 and metal is formed as an element- removal of oxygen = reduction metals more reactive than carbon are extracted using electrolysis not reduction IRON AND STEELS Iron ore is displaced with carbon in a blast furnace, iron straight from the blast furnace has limited uses- contains 96% iron and some impurities, mainly carbon- makes it brittle, although it is very hard and can't be easily compressed- when molten can be run into moulds and cast into different shapes. This cast iron is used to make wood-burning stoves, man-hole covers on roads and engines Can treat the iron to remove some of the carbon- giving us pure iron which is soft and easily shaped- to make more useful combine with tiny amounts of other elements = alloy steel is an alloy of iron- by adding elements in carefully controlled amounts, we can change the properties of steel- lots of diff types of steel.- lots of different types of steel- all are alloys of iron with carbon and/or other elements- simplest steels are carbon steels (made by removing most of the carbon from cast iron, leaving small amounts (cheapest steel))- used in bodies of cars and machinery- high carbon steel is strong but brittle- low carbon steel is soft and easily shaped (type is mild steel) low-alloy steels are more expensive because they contain between 1-5% of other metals high-alloy steels even more expensive- higher percentage of other metals- chromium nickel steel = stainless steels (cutlery)- resistant to corrosion ALUMINIUM AND TITANIUM strong and have a low density (light)- also don't corrode ALUMINIUM- silvery, shiny, light, low density, excellent conductor of energy and electricity, malleable- reactive but doesn't corrode easily due to thin layer of aluminium oxide that stops further corrosion taking place- forms alloys that are stronger, used in cooking foil and saucepans extracting aluminium- electrolysis (al oxide must be melted before electrolysis)- electrolysis is expensive (high temps to melt and extract), and not good for the environment TITANIUM- silvery, strong,  very resistant to corrosion, has an oxide layer that protects it, denser than aluminium but less dense than other metals, high melting point, used for high performance aircraft and racing bikes, parts of jet engines, nuclear reactors, replacement hip joints extracting titanium- could with carbon as less reactive than aluminium, however carbon reacts with it and turns it brittle, so use more reactive metals like sodium or magnesium (which have to be extracted through electrolysis)- takes a lot of steps to extract, takes time and costs money EXTRACTING COPPER most extracted from copper-rich ores (limited resource running out)- two methods- using sulfuric acid to produce copper sulfate solution before extracting and smelting (heating in a furnace) ex. copper sulfide + oxygen - copper + sulfur dioxide must avoid letting sulfur dioxide into the air then use impure copper as the positive electrode in electrolysis cells to make pure copper however 80% still done by smelting smelting and purifying copper ore uses huge amounts of heat and electricity- costs a lot of money and has a huge impact on the environment most copper is extracted by smelting copper-rich ores, copper can also be extracted from copper sulphate solutions by electrolysis or by displacement using scrap iron. Electrolysis is also used to purify impure copper (from smelting) scientists developing new ways to get copper from low-grade ores, use bacteria (bioleaching) and plants (phytomining) PHYTOMINING- plants absorb copper compounds from low-grade copper ore as they grow (could be from slag heaps of copper rich), plants are then burned and metals extracted from the ash (then leach using sulfuric acid then displacement with scrap iron) BIOLEACHING- bacteria feed on low-grade metal ores, by a combination of biological and chemical processes get a solution of copper ions (then scrap iron and electrolysis)  USEFUL METALS Transition metals, similar properties- strong, malleable, good conductors of electricity and energy- lots of uses copper is a transition metal- water pipes, wires copper alloys = bronze (copper and tin, resistant to corrosion), brass (copper and zinc, hard, used for musical instruments) Aluminium alloys- over 300 available gold and copper- doesnt wear away as quickly, durable, less expensive, vary proportions for different shades METALLIC ISSUES Cast mining for iron, copper and aluminium scar the landscape, creating noise and dust and destroying  the habitats of plants and animals, also leave large heaps of waste rock heating strongly and extraction - acid rain groundwter acidity as a result of water draining through exposed ores and slag heaps of waste electrolysis OR scrap iron recycling- saves money of extraction- conserves earth's reserves of metal ores steel most commonly used metal- steel girders suspension bridges, however rusts- affects strength (stainless too expensive)

CRUDE OIL AND FUELSFUELS FROM CRUDE OIL crude oil a mixture of lots of different chemical compounds (not chemically combined) separate into different fractions- fractional distillation (separates liquids with different boiling points) all compounds in crude oil are hydrocarbons- most are alkanes CnH2n+1- saturated hydrocarbons (no more hydrogen atoms can be added) FRACTIONAL DISTILLATION hydrocarbon molecules can be short chain and long chain- short chain most useful (make good fuels, burn well, very flammable, lower boiling point, more volatile, low viscosity (runny)) fractional distillation- each hydrocarbon fraction contains molecules with similar numbers of carbon atoms, each boils at diff temperature range crude oil fed in as vapour (hot at bottom , cool at top) temp decreases going up, gases condense when they reach the temp of their boiling points, smallest molecules have lowest boiling points and are collected at the top and vice versa. Once collected, fractions need more processing before they can be used lighter fractions make better fuels as they ignite more easily and burn well with cleaner less smoky flames.  BURNING FUELS carbon and hydrogen in the fuels are oxidised impurities found in fossil fuels produce additional products ( as well as CO2 and H2O) not enough oxygen in an engine, incomplete combustion, carbon monoxide is formed high temp in an engine also allows N and O in the air to react together (nitrogen oxides), poisonous and cause acid rain diesel engines burn hydrocarbons with bigger molecules, dont always burn completely with oxygen, tiny solid particulates containing carbon and unburnt hydrocarbons are produced, particulates carried into the air- might cause cancer- cause global dimming carbon monoxide is a serious pollutant- affects amount of oxygen blood is able to carry CLEANER FUELS catalytic converters- metal catalysts, large SA so carbon monoxides and nitrogen oxides react together sulfur dioxide removed by reacting it with calcium oxide or hydroxide ALTERNATIVE FUELS biofuels are fuels made from plants and animal products (biodiesel= oil extracted from plants) biodiesel breaks down faster than normal diesel, burns more cleanly, reduces particulates, CO2 neutral (pretty much) uses large areas of farmland for fuel instead of food- famine in poor countries, destruction of habitats ethanol- made by fermenting the sugar from sugar cane- carbon neutral hydrogen as a fuel- safety concerns with storage (explosive with air), takes up larger volume than liquid fuels

PRODUCTS FROM OILCRACKING HYDROCARBONS break down large hydrocarbon molecules by cracking- takes place in an oil refinery in a steel vessel called a cracker thermal decomposition takes place and large molecules split apart into smaller, more useful ones cracking produces different types of molecules- alkanes and alkenes (unsaturated double bond CnH2n) alkenes turn bromine water colourless MAKING POLYMERS FROM ALKENES use chemicals from oil to make plastics- small molecules are monomers and huge molecules they make are polymers- eg ethene to Poly(ethene) (easy to shape, strong and transparent) poly(propene) (strong, tough plastic) when alkene molecules join together, the double bond between the carbon atoms in each molecule open up and is replaced by single bonds as thousands of molecules join together (alkenes more reactive than alkanes) NEW AND USEFUL POLYMERS light sensitive plasters hydrogels- polymer chains with a few cross linking units between chains, makes a matrix than trap water shape memory polymers- example of a smart polymer (may have their properties changed by light, temperature or by other changes in their surroundings bottles made out of plastic PET can be recycled PLASTIC WASTE waste plastics last for hundreds of years before they are broken down completely- take up valuable space in landfill sites biodegradable plastics (broken down by micro-organisms) ways to speed up decomposition- using granules of cornstarch built into plastic (micro organisms feed on the starch and break up the plastic into smaller pieces more quickly) plastic carrier bags- PLA- preserves supplies of crude oil disads of biodegradable plastics- higher food prices (lack of space), famine, destruction of habitats ETHANOL made by fermentation of sugar cane, enzymes in yeast break down the sugar into ethanol and CO2 also used as a solvent ethanol for industrial use as a fuel or solvent can be made from ethene gas instead of by fermentation- reacts with steam to make ethanol = hydration requires energy to heat, reversible, continuous process, produces no waste products- relies on crude oil which is a non renewable resource fermentation is batch and CO2 is given off

fundamental ideas

rocks and building materials

metals and their uses

crude oil and fuels

products from oil