C1 1.1 Atoms
- All substances are made of atoms. A substance that is made of only one sort of atom is called an element. Elements are in the periodic table and the groups contain elements with similar properties.
- Atoms have a small nucleus in the centre, which is made up of protons and neutrons and around these are the electrons.
- Proton = +1 charge
- Neutron = 0 charge
- Electron = -1 charge
- In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
- The number of protons in an atom of an element is its atomic number. The sum of the protons and neutrons in an atom is its mass number
- Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level. The electrons in an atom occupy the lowest available energy levels.
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C1 1.2 The Periodic Table
- Elements in the same group in the periodic table have the same number of electrons in their highest energy level and this gives them similar chemical properties.
- The elements in Group 0 of the periodic table are called the noble gases. They are unreactive because their atoms have stable arrangements of electrons.
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C1 1.3 Chemical reactions
- When elements react, their atoms join with other atoms to form compounds. This involves giving, taking or sharing electrons to form ions or molecules.
- Compounds formed from metals and non-metals consist of ions.
- Metals lose electrons to form positive ions
- Non-metals gain electrons to form negative ions.
- Compounds formed from non-mentals consist of molecules.
- In molecules the atoms are held together by covalent bonds.
- Chemical reactions can be represented by word equations or symbol equations
- No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
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C1 2.1 Calcium Carbonate
- Limestone is mainly composed of the compounds calcium carbonate(CaCO3)
- It's quarried and used as a building material
- Calcium carbonate can be decomposed by thermal decomposition to make calcium oxide and carbon dioxide
- The carbonates of magnesium, copper, zinc, calcium and sodium decompose on heating in a similar way
- Calcium oxide reacts with water to produce calcium hyrdroxide which is an alkali that can be used in the neutralisation of acids.
- A solution of calcium hyrdroxide in water (limewater) reacts with carbon dioxide to produce calcium carbonate.
- Limewater is used as a test for carbon dioxide. Carbon dioxide turns limewater cloudy
- Carbonates react with acids to produce carbon dioxide, a salt and a water.
- Limestone is damaged by acid rain.
- Limestone is heated with clay to make cement.
- Cement is mixed with sand to make mortar.
- Cement is mixed with sand and aggregate to make concrete.
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C1 3.1 Extracting Metals
- Ores contain enough metal to make it economic to extract the metal. Ores are mined and may be concentrated before the metal is extracted and purified.
- Unreactive metals such as gold are found in the Earth as the metal itself, but most metals are found as compounds that require chemical reactions in order to extract the metal.
- Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon, eg iron oxide is reduced in the blast furnace to make iron.
- Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compoudns.
- The use of large amounts of energy in the extraction of these metals makes them expensive.
- Copper can be extracted from copper-rich ores by heating the ores in a furnace (smelting). The copper can be purified by electrolysis. The supply of copper-rich ores is limited.
- New ways of extracting copper from low-grade ores are being researched to limit the environmental impact of traditional mining. Copper can be extracted by phytomining or by bioleaching
- Phytomining uses plants to absorb metal compounds. The plants are burned to produce ash that contains the metal compounds. Bioleaching uses bacteria to produce leachate solutions that contain metal compounds.
- Copper can be obtained from solutions of copper salts by electrolysis or by displacement using scarp iron
- Aluminium and titanium cannot be extracted from their oxides by reduction with carbon. Current methods of extraction are expensive because: there are many stages in the process and large amounts of energy are needed
- We should recycle metals because extracting them uses limited resources and it is expensive in terms of energy and effects on the environment
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C1 3.2 Alloys
- Iron from the blast furnace contains about 96% iron. The impurities make it brittle and so it has limited uses.
- Most iron is converted into steels. Steels are alloys since they are a mixture of iron with carbon. Some steels contain other metals.
- Alloys can be designed to have properties for specific uses.
- Low-carbon steels are easily shaped, high-carbon steels are hard, and stainless steels are resistant to corrosion
- Most metals in everyday use are alloys.
- Pure copper, gold, iron and aluminium are too soft for many uses and so are mixed with small amounts of similar metals to make them harder for everyday use
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C1 3.3 Properties and Uses of Metals
- The elements in the central block of the periodic table are known as transition metals. Like other metals they are good conductors of heat and electricity and can be bent or hammered into shape. They are useful as structural materials and for making things that must allow heat or electricity to pass through them easily.
- Copper has properties that make it useful for electrical wiring and plumbing
- it is a good conductor of electricity and heat
- can be bent but is hard enough to be used to make pipes or tanks
- does not react with water
- Low density and resistance to corrosion make aluminium and titanium useful metals
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C1 4.1 Crude Oil
- Crude oil is a mixture of a very large number of compounds
- A mixture consists of two or more compounds not chemically combined together.
- The chemical properties of each substance in the mixture are unchanged.
- It is possible to separate the substances in a mixture by physical methods including distillation.
- Most of the compounds in crude oil consist of molecules made up of hydrogen and carbon atoms only (hydrocarbons)
- Most of these are saturated hydrocarbons called alkanes, which have the general formula: CnH2n+2
- You do not need to know the names of specific alkanes other than methane, ethane and propane.
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C1 4.2 Hydrocarbons
- Alkane molecules can be represented in the following forms:
H –– C –– C –– H
- The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by evaporating the oil and allowing it to condense at a number of different temperatures. This process is fractional distillation
- Some properties of hydrocarbons depend on the size of their molecules. These properties influence how hydrocarbons are used as fuels.
- boiling points
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C1 4.3 Hydrocarbon Fuels
- Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur.
- The gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, sulfur dioxide and oxides of nitrogen. Solid particles (particulates) may also be released.
- The combustion of hydrocarbon fuels releases energy. During combustion the carbon and hydrogen in the fuels are oxidised.
- Sulfur dioxide and oxides of nitrogen cause acid rain, carbon dioxide causes global warming, and solid particles cause global dimming.
- Sulfur can be removed from fuels before they are burned, eg in vehicles.
- Sulfur dioxide can be removed from the waste gases after combustion, eg in power stations.
- Bio-fuels, including bio-diesels and ethanol, are produced from plant material. There are economic, ethical and environmental issues surrounding their use.
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C1 5.1 Obtaining useful substances from crude oil
- Hydrocarbons can be cracked to produce smaller, more useful molecules.
- This process involves heating the hydrocarbons to vaporise them.
- The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur.
- The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. Alkenes have the general formula: CnH2n
- Unsaturated hydrocarbon molecules can be represented in the following forms:
- H H H
- I I I
- H –– C –– C == C (== represents a double bond)
- I I
- H H
- Alkenes react with bromine water, turning it from orange to colourless
- Some products of cracking are useful as fuels
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C1 5.2 Polymers
- Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In these reactions, many small molecules (monomers) join together to form very large molecules (polymers). For example:
- Polymers have many useful applications and new uses are being developed, eg: new packaging materials, waterproof coatings for fabrics, dental polymers, hydrogels.
- Many polymers are not biodegradable, so they are not broken down by microbes and this can lead to problems with waste disposal.
- Plastic bags are being made from polymers and cornstarch so that they can break down more easily. Biodegradable plastics made from cornstarch have been developed.
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C1 5.3 Ethanol
- Ethanol can be produced by the hydration of ethene with steam in the presence of a catalyst
- Ethanol can also be produced by fermentation with yeast, using renewable resources. This can be represented by:
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C1 6.1 Vegetable Oils
- Some fruits, seeds and nuts are rich in oils that can be extracted.
- The plant material is crushed and the oil is removed by pressing or in some cases by distillation. Water and other impurities are removed.
- Vegetable oils are important foods and fuels as they provide a lot of energy. They also provide us with nutrients.
- Vegetable oils have higher boiling points than water and so an be used to cook foods at higher temperatures than by boiling.
- This produces quicker cooking and different flavours but increases the energy that the food releases when it is eaten.
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C1 6.2 Emulsions
- Oils do not dissolve in water.
- They can be used to produce emulsions.
- Emulsions are thicker than oil or water and have many uses that depend on their special properties.
- They provide better texture, coating ability and appearance, for example in salad dressings, ice creams, cosmetics and paints.
- Emulsifiers have hydrophilic and hydrophobic properties (HT only)
- Emulsifiers have:
- A hydrophilic head - 'water loving' - that forms chemical bonds with water but not with oils
- A hydrophobic end - 'water-hating' - that forms chemical bonds with oils but not with water
- Lecithin is an emulsifier commonly used in foods. The hydrophilic 'head' dissolves in the water and the hydrophobic 'tail' dissolves in the oil. In this way, the water and oil droplets become unable to separate out.
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C1 6.3 Saturated and Unsaturated Oils
- Vegetable oils that are unsaturated contain double carbon-carbon bonds. These can be detected by bromine water.
- (HT ONLY) Vegetable oils that are unsaturated can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60°C.
- Hydrogen adds to the carbon-carbon double bonds.
- The hydrogenated oils have higher melting points so they are solids at room temperature, making them useful as spreads in cakes and pastries.
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C1 7.1 The Earth's Crust
- The Earth consists of a core, mantle and crust, and is surrounded by the atmosphere.
- crust - relatively thin and rocky
- mantle - has the properties of a solid, but can flow very slowly
- core - made from liquid nickel and iron
- The Earth's crust and the upper part of the mantle are cracked into a number of large pieces (tectonic plates)
- Convection currents within the Earth's mantle driven by heat released by natural radioactive processes cause the plates to move at relative speeds of a few centimeters per year
- The movements can be sudden and disastrous.
- Earthquakes and/or volcanic eruptions occur at the boundaries between tectonic plates.
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C1 7.2 The Earth's Atmosphere
- For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:
- about four fifths (80%) nitrogen
- about one fifth (20%) oxygen
- small proportions of various other gases, including carbon dioxide, water vapour and noble gases.
- During the first billion years of the Earth's existence, there was intense volcanic activity. This activity released the gases that formed the early atmosphere and water vapour that condensed to form the oceans.
- There are several theories about how the atmosphere was formed.
- One theory suggests that during this period the Earth's atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas (like the atmospheres of Mars or Venus today). There may also have been water vapour and small proportions of methane and ammonia
- There are many theories as to how life was formed billions of years ago
- One theory as to how life was formed involves the interaction between hydrocarbons, ammonia and lightning. (HT only)
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C1 7.2 The Earth's Atmosphere (continued)
- Plants and algae produced the oxygen that is now in the atmosphere by photosynthesis
- Most of the carbon from carbon dioxide in the air gradually became locked up in sedimentary rocks as carbonates and fossil fuels
- Limestone was formed from the shells and skeletons of marine organisms. Fossil fuels contain carbon and hydrocarbons that are the remains of plants and animals.
- The oceans act as a reservoir for carbon dioxide but increased amounts of carbon dioxide absorbed by the ocean has an impact on the marine environment.
- Nowadays the release of carbon dioxide by burning fossil fuels increases the level of carbon dioxide in the atmosphere. This is thought to be causing global warming.
- Air is a mixture of gases with different boiling points and can be fractionally distilled to provide a source of raw materials used in a variety of industrial processes. (HT only)
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C1.7 The Miller-Urey Experiment
- The aim of this experiment was to see if substances now made by living things could be formed in the conditions thought to have existed on the early Earth.
- They sealed a mixture of water, ammonia, methane and hydrogen in a sterile flask.
- The mixture was heated to evaporate water to produce water vapour.
- Electric sparks were passed through the mixture of water vapour and gases, simulating lightning.
- After a week, contents were analysed.
- Amino acids, the building blocks for proteins were found.
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C1.7 The Miller-Urey Experiment diagram
- The Miller-Urey experiment supported the theory of a ‘primordial soup’, the idea that complex chemicals needed for living things to develop could be produced naturally on the early Earth.
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