Atoms and Elements
Element- Substance made up of one atom.
An atom has a central nucleus containing protons and neutrons. The nucles is then surrounded by smaller sub-atomic particles called electrons which occupy energy levels/shells.
- Proton- Positive
- Neutron- Neutral
- Electron- Negative
- The number of electrons is always equal to the number of protons so the overall charge of an atom is neutral (no electrical charge).
The atomic number of an atom is the number of protons it contains. The mass number of an atom is the total number of protons and neutrons it contains.
Energy levels can only hold a specific number of electrons. On the first shell: 2; on the second: 8; and on the third: 8. When you write the electronic configuration you write the number of electrons on each energy level. For example, Chlorine's electronic configuration is 2,8,7.
The Periodic Table
The Periodic Table is a chart with all the elements arranged in a particular way. The metals are on the left on the table, the non-metals on the right.
A vertical column in the table is called a group. The elements in the same group have similar chemical properties. For example, Group 1 is very reactive, whereas Group 0 (Noble Gases) are very unreactive. The number of the group depends on how many electrons on the atom's outer shell.
The elements in Group 1 are very reactive as they have 1 electron on their outer shell which makes them very unstable as they are looking to bond with another element in order for them to gain a full outer shell.
The elemnts in Group 0 are very unreactive as they have a full outer shell which makes them very stable.
When elements react, they join to other elements to form compounds. These bonds are formed when atoms share/ transfer their electrons.
Ionic takes place between a non-metal and a metal. The metal atom loses an electron to form positive ions and the non-metal gains the metal's spare electron to form negative ions. These oppostite charges attract and join together forming an ionic bond. This happens so both elements can have a full outer shell.
A compound formed from non-metals consists of molecules. Each atom shares an electron with another atom, therefore each atom has enough electrons to fill its outer shell.
No atoms are lost or made during a reaction. Therefore, the mass is conserved.
The Lime Cycle
- Calcium Carbonate (CaCO3) breaks down when heated (thermal decomposition) to form Calcium Oxide (CaO) and Carbon Dioxide. Metals high up in the reactivity series need a lot of energy to decompose, unlike those at the bottom of the series.
- Calcium Oxide reacts with water to produce Calcium Hydroxide Ca(OH)2. This is used to neutralise acidic soils.
- Calcium Hydroxide (limewater) can be a test for carbon dioxide. If you make limewater and bubble gas through it, the solution will go cloudy if carbon dioxide is present. This is due to the formation of Calcium Carbonate (Limestone).
Uses- Powdered Limestone is heated in a kiln with powdered clay to make cement. Cement can be mixed with sand and water to make mortar. Or add aggregate to make concrete.
Advantages and Disadvantages of Quarrying
- Noise, dust and vehicle pollution
- Destroys habitats
- Waste materials are dumped
- Creates jobs
- Makes useful materials
- Boosts economy
The Reactivity Series
The Earth' crust contains metals and metal compounds called ores. A metal ore is a rock containing a metal. The metal is extracted depending on its reactivity.
- Metals higher than carbon in the reactivity series are extracted via electrolysis (Potassium, Sodium, Calcium, Magnesium, Aluminium)
- Metals higher than hydrogen, but lower that carbon are extracted via reactions with carbon or carbon monoxide (Zinc, iron, Tin, Lead)
- Metals lower than hydrogen are extracted in other ways (Copper, Silver, Gold, Platinum) Gold is so unreactive, it is found a native metal and not as a compound.
Transition Metals- Placed in the middle of the periodic table between group 2 and 3. Most metals are transition metals. They are good conductors and can be hammered or bent into shape easily.
- Electroysis- Splitting up with electricity. It requires a liquid to conduct the electricity, called the electrolyte which has free ions which conduct electricity. Electrons are taken away by the positive anode and negative cathode. The positive copper ions are attracted to the negative cathode and turn back into copper atoms whilts impurites at the anode is dropped as sludge.
- High-grade copper ores are running out so other methods are being developed.
- Bioleaching- Some bacteria absorb copper compounds. They then produce solutions called leachates, which contain copper compounds
- Phytomining- Some plants absorb copper compounds through their roots. They concentrate these compounds as a result of this. The plants can be burned to produce an ash that contains the copper compounds.
Iron is extracted from iron ore in a blast furnace. Iron ores such as haematite contain iron oxide. The oxygen must be removed so it is called a reduction reaction.
- Carbon is more reactive than iron so it can displace the iron from the iron oxide.
- Carbon+Iron Oxide - Carbon Dioxide+Iron (Carbon has been oxidised and Iron reduced so it's called a redox reaction)
- 3C+2Fe203 - 3CO2+4F
Aluminium and Titanium
Aluminium and Titanium are low density metals which means they are lightweight for their size. hey also have a very thin layer of their oxides on the surface, which stops air and water getting to the metal, so aluminium and titanium resist corrosion.
Aluminium is used for aircraft, trains, overhead power cables, saucepans and cooking foil.
Titanium is used for fighter aircrafts, artificial hip joints and pipes in nuclear power stations.
Unlike iron, aluminium and titanium cannot be extracted from their oxides by reduction with carbon. The process is very long, requires lots of energy and is very expensive.
Recycling aluminium is important and it requires les energy to extract recycled aluminium than aluminium from its ore. Recycling preserves limited resources and causes less damage to the environment as it uses less energy.
Alloys and Iron and Steel
The properties of a metal are changed by adding other elements to it. A mixture of two or more elements, where at least one element is a metal, is called an alloy. Alloys are harder than pure metals as the pattern becomes distorted so it doesn't slip and slide. For example:
- Brass (70% copper, 30% zinc)- used in electrics
- 18 carat gold (75% gold, 25% copper)- used for jewellery
- Duralumin (96% aluminim, 4% copper and other metals)- used in aircrafts.
Iron and Steel
Pure iron is too soft for many uses as the particles are in a regular order and slip and slide over each other. Iron from the blast furnace is an alloy of 96% iron and 4% carbon. It's hard but too brittle. Carbon is removed by blowing oxygen into it which reacts with the carbon forming Carbon Dioxide and Carbon Monoxide. Enough oxygen is used until the right amount of carbon remains:
- Low Carbon Steel- 0.25% carbon, easily shaped, used for car panels
- High Carbon Steel- 2.5% carbon, hard, used for cutting tools.
- Stainless Steel- alloied with chromium and nickel, resists corrosion, used for cutlery and sinks.
Separating Crude Oil
Alkanes- Type of crude oil that is a hydocarbon (hydorgen and carbon covalent bond) All alkanes share the general formula: CnH2n+2. The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two. Alkanes are saturated- each carbon atom is joined to 4 other atoms.
Distillation- Separate a liquid from a mixture of liquids. Only works when the liquids have different boiling points. It is used to separate Ethanol from water. Ethanol has a lower boiling point than water so it evaporates quicker. The Ethanol vapour then cools and condenses to form pure Ethanol. When all the Ethanol evaporates, the temperate rises as the water begins to evaporate.
Fractional Distillation- Fractional distillation is different from distillation in that it separates a mixture into a number of different parts, called fractions. A fractional distillation happens in a large column split into sections. The column is hot at the bottom and cool at the top. Crude oil is heated at the bottom until it reaches its boiling point when it evaporates. The vapour travels up the column until it reaches its boiling point where it starts to condense and is collected. The boiling point depends on the length of the hydrocarbon chain. Small molecules have a low boiling point, they are easy to light (volatile) and they flow. Whereas, large molecules have the opposite properties.
Hydocarbons as Fuels
Alkenes- Unsaturated molecules that have at least 1 carbon double bond. You text for alkenes by adding Bromine Water which will go from orange to colourless if an alkene is present. General Formula: CnH2n and they are used to make polymers (plastics made by identical repeating monomers)
Supply and Demand- Crude Oil contains many long chain hydrocarbons which are not useful or valuable unlike short chain hydrocarbons which are high in demand but low in supply. Catalytic Cracking breaks large hydrocarbons into smaller molecules by using heat (thermal decomposition) and a catalyst (speeds up a reaction) For example- Octane (C8H18) goes to Ethene (C2H4) + Hexane (C6H14)
Combustion- Fuels burn when they react with oxygen in the air. If there is plenty of air, complete combustion happens. carbon+oxygen - carbon dioxide. Hydrocarbon fuels contain carbon and hydrogen. During combustion, hydrogen is oxidised to water (hydrogen+carbon - carbon dioxide + water). If insufficient oxygen is available, carbon monoxide is the product (toxic) - this is called Incomplete Combustion.
Acid Rain- Sulfur burns to produce sulfur dioxide which dissolves in water vapour and cause acid rain.
Biofuels- Biofuels are renewable unlike crude oil and it does not release pollutants like crude oil does (carbon dioxide, particulates, carbon monoxide, sulfur dioxide). It is also carbon neutral, however it takes longer to make and increases manual labour.
Polymers and Ethanol
Polymers- Made by repeating, identical monomers joining together. When a polymer is formed, the double bond breaks. Different polymers have different uses:
- Polythene- Plastic bags and bottles
- Polypropene- Crates and ropes
- Polychloroethene- Water pipes and insulation on energy cables
Problems- They are very unreactive so it makes it difficult to dispose of them as they are not biodegradable. However, many polymers can be recycled which reduces the problem.
Ethanol (C2H2OH) can be produced two ways-
- Fermentation (yeast and sugar)- renewable, needs low temperatures. However, it produces impure ethanol that needs to be distilled, it is a batch process (stops and starts) and it is a slow reaction.
- Hydration (Ethene and steam)- non-renewable, needs high temperatures. However, it produces pure ethanol and it is a continuous process that happens quickly.
Some fruits and seeds contain a lot of oil which is squeezed an pressed against metal plates to get the oil out. More difficult plants have to be dissolved in a solvent then the solution is distilled to remove impurities.
- Cooking- Vegetable oils have higher boiling points than water which mean that they can cook our food at higher temperatures and at faster speeds and it has a different flavour.
- Food- Vegetable oils contain lots of energy and Vitamin E. However, this can make us overweight.
- Fuels- Processed into fuel
Saturated and Unsaturated Fats- The fatty acids in some vegetable oils are saturated: they only have single bonds between their carbon atoms. Saturated oils can be solid at room temperature and called vegetable fats. The fatty acids in some vegetable oils are unsaturated (healthier): they have double bonds between some of their carbon atoms. Monounsaturated fats (1 double bond), Polyunsaturated fats (many double bonds)
Emulsions- Vegetable oils do not dissolve in water as they are more viscous. If an emulsion is left to stand the oil will form a layer at the top. Emulsifiers are substances that stabilise emulsions, stopping them separating out.
Hydrophilic emulsifier ends form bond with water, not oil. Unlike Hydrophobic ends which do the opposite.
Double Bonds and Hydrogenation
Bromine Water Test- Unsaturated vegetable oils contain double carbon-carbon bonds. These can be detected using bromine water (just as alkenes can be detected). It goes from orange to colourless with an unsaturated fat, but stays the same when shaken with a saturated fat.
Hydrogenation- Saturated vegetable fats are solid at room temperature, and have a higher melting point than unsaturated oils. Unsaturated vegetable oils can be ‘hardened’ by reacting them with hydrogen, a reaction called hydrogenation. During hydrogenation, vegetable oils are reacted with hydrogen gas at about 60ºC. A nickel catalyst is used to speed up the reaction. The double bonds are converted to single bonds in the reaction.
The Earth's Crust
The Earth's Crust (outermost first)-
- Crust- Thin and rocky
- Mantle- Properties of a solid, but can flow very slowly
- Core- Made from liquid nickel and iron
Plate Tetonics- The Earth's crust and upper mantle are broken into large pieces called tetonic plates which move constantly, a few centimetres every year (continental drift). They move becase of the radiactive decay that takes place in the mantle which causes convection currents. There are two main types of tetonic plates: Oceanic and Continental. Oceanic plates are denser.
Where tetonic plates meet, the Earth can become unstable as the plates push against each other. This can cause Earthquakes and Volcanic Eruptions which are very difficult to predict. However, there a few clues to say that a volcanic eruption might happen- molten rock rising into chambers near the surface causing the Earth to bulge.
Wegener- Wegener suggested that mountains were formed when the edge of a drifting continent collided with another, causing it to crumple and fold. It took more than 50 years for his theory to be accepted as it was difficult to work out how whole continents could move: it was not until the 1960s that enough evidence was discovered to support the theory fully. Before Wegener developed his theory, it was thought that mountains formed because the Earth was cooling down, and in doing so contracted.
Modern Atmosphere- 21% oxygen 78% nitrogen and traces of water vapour, carbon dioxide and other noble gases.
The Early Atmosphere- Scientists believe Earth was formed 4.5 billion years ago. The early atmosphere was mostly carbon dioxide with little or no oxygen due to the intense volcanic activity. The atmosphere in Mars and Venus today are similar to Earth's early atmosphere.
Life on Earth- It is believed life began around 3 billion years ago. The primordial soup theory states that billions of years ago, Earth's atmosphere was nitrogen, hydrogen, ammonia and methane. Lightning struck, causing chemical reactions forming aminio acids that collected in 'primordial soup' (body of water) which then produced organic matter. In the 1950's Miller and Urey carried out an experiement to prove this. They sealed gases and applied an electrical charge for a week. They found amino acids were made, but not as many which suggests the theory was along the right lines.
- Increasing Oxygen- Plants and algae carry out photosynthesis which is released into the atmosphere.
- Decreasing Carbon Dioxide- Photosynthesis, dissolving in oceans, producing sedimentary rocks.
- Distilling Air- Air is filtered to remove dust, and then cooled in stages until it reaches –200°C. At this temperature it is a liquid. We say that the air has been liquefied: 1)Water vapour condenses, and is removed using absorbent filters. 2)Carbon dioxide freezes at –79ºC, and is removed. It is then passed into a fractional distillating column, the nitrogen boils and rises, argon and oxygen collect at the bottom and another column is used to separate them.