GCSE Chemistry Unit 1 Key Points

Key points from AQA textbook.

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C1: Fundamental ideas:

C 1.1. Atoms, elements and compounds:

·         All substances are made up of atoms.

·         Elements contain only one atom.

·         Compounds contain more than one atom.

·         An atom has a tiny nucleus in its centre, surrounded by electrons.

C 1.2. Atomic structure:

·         Atoms are made up of protons, neutrons and electrons.

·         Protons and electrons have equal and opposite electrical charges. Protons are positively charged, and electrons are negatively charged.

·         Neutrons have no electrical charge. They are neutral.

·         Atomic number = number of protons (number of electrons.)

·         Mass number = number of protons and neutrons.

·         Atoms are arranged in the periodic table in order of their atomic number.

C 1.3. The arrangement of electrons in atoms:

·         The electrons in an atom are arranges in energy levels or shells.

·         Atoms with the same number of electrons in their outermost shell belong in the same group of the periodic table.

·         The arrangement of electrons in the outermost shell of an elements atom determines the way that element reacts.

·         The atoms of the unreactive noble gases (in group 0) all have very stable arrangements of electrons.

C 1.4. Forming bonds:

·         When atoms from different elements react together they make compounds. The formula of a compound shows the number and type of atoms that have bonded together to make that compound.

·         When metals react with non-metals, charged particles called ions are formed.

·         Metal atoms form positively charged atoms. Non-metals form negatively charged atoms. These oppositely charged ions attract each other in ionic bonding.

·         Atoms of non-metals bond to each other by sharing electrons.  This is called covalent bonding.

C 1.5. Chemical equations:

·         As no new atoms are ever created or destroyed in a chemical reaction: total mass of reactants = total mass of products.

·         There is the same number of each type of atom in each side of a balanced symbol equation.

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C 2: Rocks and building materials:

C 2.1. Limestone and its uses:

·         Limestone is made mainly of calcium carbonate.

·         Limestone is widely used in the building industry.

·         The calcium carbonate in limestone breaks down when we heat it strongly to make calcium oxide and carbon dioxide. The reaction is called thermal decomposition.

C 2.2. Reaction of carbonates:

·         Carbonates react with dilute acid to form a salt, water and carbon dioxide.

·         Limewater turns cloudy in the test for carbon dioxide gas. A precipitate of insoluble calcium carbonate causes the cloudiness.

·         Metal carbonates decompose on heating to form the metals oxide and carbon dioxide.

C 2.3. The ‘limestone reaction cycle’:

·         When water is added to calcium oxide it produces calcium hydroxide.

·         Calcium hydroxide is alkaline so it can be used to neutralize acids.

·         The reactions of limestone that you need to know are shown in the limestone cycle.

C 2.4. Cement and concrete:

·         Cement is made by heating limestone with clay in a kiln.

·         Mortar is made by mixing cement and sand and water.

·         Concrete is made by mixing crushed rocks or small stones called aggregate, cement and sand with water.

C 2.5. Limestone issues:

·         There are good and bad points about quarrying for limestone. For example, more jobs will be created, but it will leave a large scar on the landscape.

·         Limestone cement and concrete all have useful properties for use as building materials, but the mining and processing of limestone and its products has a major effect on our environment.

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C 3: Metals and their uses:

C 3.1. Extracting metals:

·         A metal ore contains enough of the metal to make it economic to extract the metal. Ores are mined and might need to be concentrated before the metal is extracted and purified.

·         We can find gold and other unreactive metals in their native state.

·         The reactivity series helps us to decide the best way to extract a metal from its ore. The oxides of a metal below carbon in the series can be reduced by carbon to give the metal element.

·         The metals more reactive than carbon cannot be extracted from their ores using carbon.

C 3.2. Irons and steels:

·         We extract iron from iron ore by reducing it using carbon in a blast furnace.

·         Pure iron is too soft for it to be very useful.

·         Carefully controlled quantities of carbon and other elements are added to iron to make alloys of steel with different properties.

·         Important examples of steels are:

o   Low carbon steels, which are easily shaped.

o   High carbon steels,  which are very hard

o   Stainless steels, which are resistant to corrosion.

C 3.3. Aluminum and titanium:

·         Aluminum and titanium are useful because they are resistant to corrosion.

·         Aluminum requires the electrolysis of molten aluminum oxide to extract it as it is too reactive to reduce it using carbon.

·         Aluminum and titanium are expensive because extracting them from their ores involves many stages and requires large amounts of energy.

C 3.4. Extracting copper:

·         Most copper is extracted by smelting (roasting) copper rich ores, although our limited supplies of ores are becoming scarce.

·         Copper can be extracted from copper solutions using electrolysis or by displacement using scrap iron.

·         Scientists are developing ways to extract copper that use low-grade copper ores. Bacteria are used in bioleaching and plants in phytomining.

C 3.5. Useful metals:

·         The transition metals are found in the central block of elements in the periodic table.

·         Transition metals have properties to make them useful for building and making things. For example, copper is used in wiring because of its high electrical conductivity.

·         Copper, gold and aluminum are all alloyed with other metals to make them harder.

C 3.6. Metallic issues:

·         There are social and environmental issues associated with exploiting ores.

·         Plants can remove metals from low grade ores. The metal can be recovered by processing the ash from burning the plants.

·         Recycling metals saves energy and our limited metal ores (and fossil fuels). The pollution from extracting metals is also reduced.

·         There are drawbacks as well as benefits from the use of metals in structures.

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C 4: Crude oil and fuels:

C 4.1. Fuels from crude oil:

·         Crude oil is a mixture of many different compounds.

·         Many of the compounds in crude oil are hydrocarbons – they contain only hydrogen and carbon.

·         Alkenes are saturated hydrocarbons. They contain as many hydrogen atoms as possible in their molecules.

C 4.2. Fractional distillation:

·         We separate crude oil into fraction using fractional distillation.

·         The properties of each fraction depend on the size of their hydrocarbon molecules.

·         Lighter fraction make better fuels as they ignite more easily and burn well, with cleaner (less smoky) flame.

C 4.3. Burning fuels:

·         When we burn hydrocarbon fuels in the air the carbon and hydrogen in the fuel are completely oxidized. They produce carbon dioxide and water.

·         Sulfur impurities in fuels burn to form sulfur dioxide which can cause acid rain.

·         Changing the conditions in which we burn hydrocarbon fuels can change the products made.

·         In insufficient oxygen we get poisonous carbon monoxide gas formed. We can also get particulates of carbon (soot) and unburnt hydrocarbon s especially if the fuel is diesel.

·         At high temperatures in engines, nitrogen from the air reacts with oxygen to form nitrogen oxides. These cause breathing problems and can cause acid rain.

C 4.4. Cleaner fuels:

·         Burning fuels releases substances that spread throughout the atmosphere.

·         Sulfur dioxide and nitrogen oxides dissolve in droplets of water in the air and react with oxygen, and then fall as acid rain.

·         Carbon dioxide produced from burning fuels is a greenhouse gas. It absorbs energy which is lost from the surface of the earth by radiation.

·         The pollution produced by burning fuels may be reduced by treating the pollutants from combustion. This can remove substances like nitrogen oxides, sulfur dioxide and carbon monoxide.

·         Sulfur can also be removed from fuels before we burn them to prevent sulfur dioxide gas being formed.

C 4.5. Alternative fuels:

·         Biofuels are a renewable source of energy that could be used to replace some fossil fuels.

·         Biodiesel can be made from vegetable oils.

·         There are advantages and disadvantages in using biodiesel.

·         Ethanol is also a biofuel as it can be made from the sugar in plants.

·         Hydrogen is a potential fuel for the future.

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C 5: Products from oil:

C 5.1. Cracking hydrocarbons:

·         We can split large hydrocarbon molecules up into smaller molecules by:

o   mixing them with steam and heating them to a high temperature, or

o   by passing them over a hot catalyst

·         Cracking produces saturated hydrocarbons which are used as fuels and unsaturated hydrocarbons (called alkenes).

·         Alkenes react with orange bromine water, turning it colourless.

C 5.2. Making polymers from alkenes:

·         Plastics are made up of polymers.

·         Polymers are large molecules made when monomers (small, reactive molecules) join together. The reaction is called polymerization.

C 5.3. New and useful polymers:

·         New polymers are being developed all the time. They are designed to have properties that make them specially suited for certain uses.

·         Smart polymers may have their properties changed by light, temperature or by other changes in their surroundings.

·         We are now recycling more plastics and finding new uses for them.

C 5.4. Plastic waste:

·         Non-biodegradable plastics cause unsightly rubbish, can harm wildlife and take up space in landfill sites.

·         Biodegradable plastics are decomposed by the action of microorganisms in soil. Making plastics with starch granules in their structure help the microorganisms break down a plastic.

·         We can make biodegradable plastics from plant material such as cornstarch.

C 5.5. Ethanol:

·         Ethanol can be made from ethane reacting with steam in the presence of a catalyst. This is called hydration.

·         Ethanol is also made by fermenting sugar (glucose) using enzymes in yeast. Carbon dioxide is also made in this reaction.

·         Using ethene to make ethanol needs non-renewable crude oil as its raw material, whereas fermentation uses renewable plant material.

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C 6: Plant oils

C 6.1. Extracting vegetable oil:

·         Vegetable oils can be made from plants by pressing, or by distillation.

·         Vegetable oils provide nutrients and have a high energy content. They are important foods and can be used to make biofuels.

·         Unsaturated oils contain carbon-carbon double bonds (C=C). We can detect them as they decolourise bromine water.

C 6.2. Cooking with vegetable oils:

·         Vegetable oils are useful in cooking because of their high boiling points. However, this increases the energy content of foods compared with cooking in water.

·          Vegetable oils are hardened by reacting them with hydrogen to increase their melting points. This makes the solids at room temperature which are suitable for spreading.

·         The hardening reaction takes place at 60% with a nickel catalyst. The hydrogen adds onto the C=C bonds in the vegetable oil molecules.

C 6.3. Everyday emulsions:

·         Oils do not dissolve in water.

·         Oil and water can be dispersed (spread out) in each other to produce emulsions which have special properties.

·         Emulsions made from vegetable oils are used in many foods, such as salad dressings, ice creams, cosmetics and paints.

·         Emulsifiers stop oil and water from separating out into layers.

·         An emulsifier works because one part of its molecule dissolves in oil (hydrophobic part) and the other part dissolves in water (hydrophilic part).

C 6.4. Food issues:

·         Vegetable oils are high in energy and provide nutrients. They are unsaturated and believed to be better for your health than saturated animal fats and hydrogenated vegetable oils.

·         Emulsifiers improve the texture of foods enabling oil and water to mix. This makes fatty food more palatable and tempting to eat.

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C 7: Our changing planet:

C 7.1. Structure of the earth:

·         The earth consists of a series of layers. Starting from the surface we have the crust, the mantle then the core in the centre. A thin layer of gases called the atmosphere surrounds the earth.

·         The earths limited resources come from the crust, the oceans, and the atmosphere.

C 7.2. The restless earth:

·         The earth’s crust and upper mantle is cracked into a number of massive pieces (tectonic plates) which are constantly moving slowly.

·         The motion of the tectonic plates is caused by convection current s in the mantle, due to radioactive decay.

·         Earthquakes and volcanoes happen where tectonic plates meet. It is difficult to know when the plates may slip past each other. This makes it difficult to predict accurately when and where earthquakes will happen.

C 7.3. The earth’s atmosphere in the past:

·         The earth’s early atmosphere was formed by volcanic activity.

·         It probably consisted mainly of carbon dioxide. There may also have been water vapour with traces of methane and ammonia.

·         As plants spread over the earth, the levels of oxygen in the atmosphere increased.

C 7.4. Life on earth:

·         One theory states that the compounds needed for life on earth came from reactions involving hydrocarbons, such as methane and ammonia. The energy required for the reaction could have been provided by lightning.

·         All the theories about how life started on earth are unproven. We can’t be sure about the events that resulted in the first life-forms on earth.

C 7.5. Gases in the atmosphere:

·         The main gases in the earth’s atmosphere are oxygen and nitrogen.

·         About four-fifths (80%) of the atmosphere is nitrogen, and about one-fifth (20%) is oxygen.

·         The main gases in the air can be separated by fractional distillation. These gases are used in industry as useful raw materials.

C 7.6. Carbon dioxide in the atmosphere:

·         Carbon moves into and out of the atmosphere due to plants, animals, the oceans and rocks.

·         The amount of carbon dioxide in the earth’s atmosphere has risen in the recent past, largely due to the amount of fossil fuels we now burn.

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