- All substances are made up of atoms.
- Elements contain only one type of atom.
- Elements are orgainsed into columns called groups.
- Compounds contain more than one type of atom.
- An atom has a tiny nucleus in its centre, surrounded by electrons.
- The nucleus contains protons and neutrons.
- The number of protons is the same as the number of electrons. They have equal and opposite charges.
- Protons have a positive charge of +1
- Electrons have a negative charge of -1
- Neutrons are neutral (have no charge).
- An atom is neutrally charged because of the balance of electron and proton charges.
- Atomic number = number of protons (number of electrons)
- Mass number = number of protons + neutrons.
- Atoms are arranged on the periodic table in order of their atomic number.
- The electrons in an atom are arranged in energy levels or shells. The innermost shell has space for 2 electrons and the rest have 8 spaces.
- Groups in the periodic table are organised in order of how many electrons are on the outermost shell of an atom, e.g. Oxygen is in Group 6 as it has 6 electrons on its outermost shell, but its atomic number is 8 because the inner shell has 2.
- The number of electrons in the outermost shell of an element's atom determines how that element reacts.
- The atoms of the unreactive Noble Gases (Group 0) all have very stable arrangements of electrons because their outer shell is entirely full, so they do not have to bond to be stable.
- 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, they become CHARGED. This is because they've transferred an electron. These charged atoms are known as ions.
- Some elements react together by transferring electrons to form chemical bonds; this occurs between metals and non-metals (ionic bonding).
- Some elements react together by sharing electrons to form chemical bonds; this occurs between two non-metals (covalent bonding).
- Metal atoms form positively charged ions because they have lost a negative electron.
- Non-metal atoms form negatively charged ions. This is because they've gained a negative electron.
- In chemical reactions, no atoms are created or destroyed. Therefore: Total mass of reactants = total mass of products.
- In a balanced symbol equation, there is the same number of each type of atom on either side.
- Chemical equations show the reactants and the products, for example:
hydrogen + oxygen = water
- Limestone is a rock mainly made of calcium carbonate.
- Powdered limestone can be heated with powdered clay to make cement.
- Cement mixed with water and aggreate produces concrete.
- Heating limestone causes thermal decomposition, and produces calcium oxide as carbon dioxide is released.
- To make a large quanitity of calcium oxide, this reaction is done in a furnance called a lime kiln. We fill the kiln and heat it strongly using a supply of hot air. Calcium oxide comes out the bottom and the waste gases (including carbon dioxide) leave the kiln at the top.
- The kiln is often rotary. This is to make sure the limestone is thoroughly mixed with the stream of hot air and ensures the limestone decomposes completely.
- Limestone is widely used in the building industry. However, buildings and statues made from limestone suffer badly from damage caused by acid rain.
- When limestone reacts with acid, it gives off a gas. To test if it is carbon dioxide, you should bubble it through a limewater solution. If it is carbon dioxide, the limewater will turn cloudy as a white precipitate is formed (calcium carbonate).
- Carbonates react with dilute acid to form a salt, water and carbon dioxide.
- Metal carbonates decompose on heating to form the metal oxide and carbon oxide.
- When water is added to calcium oxide, it produces calcium hydroxide.
- Calcium hydroxide is alkaline so it can be used to neutralise acids.
The 'Limestone Reaction Cycle':
1. Calcium Carbonate (Limestone)
HEATED, CARBON DIOXIDE GIVEN OFF
2. Calcium Oxide
3. Calcium Hydroxide
ADD MORE WATER AND FILTER
4. Calcium Hydroxide Solution
ADD CARBON DIOXIDE
5. Back to 1, and repeat.
- Cement is made by heating powdered limestone and powdered clay in a kiln.
- Mortar is made by mixing cement and sand with water.
- Concrete is made by mixing crushed rocks or small stones (aggregate), cement and sand with water.
Pros of Limestone Quarrying:
- Creates jobs working on the sites
- Creates more business for local shops with more workers around
- Creates plenty of building materials
- Roads may be improved with the larger use of them
Cons of Limestone Quarrying:
- Destroys habitats for local wildlife
- Dust from blasting may settle on crops and lower the yield
- Sound pollution
- Visual pollution
- Metals are found in the Earth's crust, most often chemically combined with other elements. Therefore it needs to be chemically separated before you can use it.
- A metal ore contains enough of the metal to make it economically and environmentally worth extracting.
- 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 decide the best way to extract a metal from its ore. The oxides of metals below carbon can be reduced to give the metal element, because the carbon and oxygen react together.
- Metals more reactive than carbon cannot be extracted from their ores using carbon. They must be extracted using electrolysis.
- Iron is extracted in a blast furnace.
iron(iii) oxide + carbon = iron + carbon dioxide
- Cast iron is 96% iron, and most of the rest is carbon. This makes it very brittle, but hard and can't be easily compressed.
- We can treat iron from the blast furnace to remove some of the carbon.
- Pure iron is very soft and easily-shaped, however is too soft for most uses.
- Alloys are metals mixed with other elements. Iron alloys can be incredibly strong, e.g. steel.
- Low carbon steel is not as strong as cast iron, but it less likely to shatter on impact with a hard object.
- Mild carbon steel is easily pressed into shape so is useful in mass production, e.g. car bodies.
- Stainless steels are resistant to corrosion.
- Aluminium and titanium are useful because they resist corrosion.
- Aluminium requires the electrolysis of molten aluminium oxide to extract it as it is too reactive to reduce using carbon.
- Aluminium and titanium are expensive because extracting them from their ores involves many stages and requires large amounts of energy.
Uses of aluminium:
- drinks cans
- cooking foil and saucepans
- high voltage electricity cables
- aeroplanes, bicycles and space vehicles
Uses of titanium:
- Bodies of racing bikes and high-performance aircrafts (strong, low density).
- Parts of jet engines (it keeps its shape even at high temps).
- Replacement hip joints (low density, strong, and resistant to corrosion.
- Most copper is extracted by smelting (roasting) copper-rich ores, although our limited supplies of ores are becoming more scarce, and are in danger of running out.
- Another method is using sulfuric acid to produce copper sulfate solution, before extracting the copper.
- Copper can be extracted from copper solutions by electrolysis or by displacement using scrap iron.
- Electrolysis can also be used to purify copper gained from processes such as smelting.
- Bioleaching and Phytomining can be used on low-grade metal ores to be more economic.
- Bioleaching is the process of bacteria feeding on low-grade metal ores, and through a combination of biological and chemical processes, we can get a solution of copper ions called a 'leachate' from waste copper ore. We can then use scrap iron and electrolysis to extract the copper.
- Phytomining is th process of growing plants on waste copper-rich ores. The plants absorb the copper ions, and are then harvested and burnt, with the metal extracted from the ashes. Copper ions can be dissolved from the ash byadding sulfuric acid, making a solution of copper sulfate. Then we can use displacement by scrap iron and electrolysis to extract pure copper metal.
- Transition metals are found in the middle/central block of the periodic table, and many have similar properties.
- Transition metals are very good conductors od electricity and other energy, like all metals. They're also strong, but can be bent/hammered into useful shapes.
- Copper is ideal for electricity wires and pipes that will carry water (can be bent into shapes but is strong enough to carry water, and doesn't react with water).
- Copper, gold, and aluminium are all alloyed with other metals to make them harder/stronger.
- There are social, economic and environmental issues associated with exploiting metals ores, e.g. the huge pits that scar the landscape, noise and dust pollution, destruction of habitats and large heaps of waste rock.
- Recycling metals saves energy and our limited metal ores (and fossil fuels used to extract them). The pollution from extracting metals is also reduced.
- There are drawbacks as well as benefits (e.g. thick steel cables used in suspension bridges are crucial to the strong structure) from the use of metals in structures, e.g. iron and steel can rust, severely weakening structures, and metals are much more expensive than other building materials such as concrete.
- Crude oil is a dark, smelly liquid which is made up of a mixture of many different compounds.
- Crude oil straight from the ground has many substances in it, all with different boiling points. Therefore, we need to separate the mixture into different substances with similar boiling points. These are called fractions.
- We can separate the different fractions through a process of distillation.
- Many of the componds in crude oil are hydrocarbons; this means they contain only hydrogen and carbon.
- Most hydrocarbons in crude oil are alkanes, e.g. methane (C H4), ethane (C2 H6).
- The general formulae for alkane molecules can be written as CnH(2n+2).
- We describe alkanes as saturated hydrocarbons. This means they have as many hydrogen atoms as possible in every molecule, no more hydrogen atoms can be added.
- Hydrocarbon molecules can be very short chains and extremely flammable, which makes them very useful for fuels with cleaner flames.
- Other hydrocarbons can be very long and have many carbon atoms, and may even have branches or side chains.
- The boiling point of a hydrocarbon depends on the size of its molecules.
- Lower boiling point
- Higher volatility (the tendancy to turn into gas)
- Low viscosity (very runny, easily flows)
- Very flammable.
- Higher boiling point
- Lower volatility
- Thick viscosity
- Not as flammable (has a smoking flame)
- Carbon dioxide and water are produced when hydrocarbons burn in plenty of air.
- The hydrogens and carbons are oxidised fully this way, meaning oxygen is added to a chemical reaction in which oxides are formed.
- 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 a poisonous carbon monoxide gas formed. We can also get particulates of carbon (soot) and unburnt hydrocarbons, especially if the fuel is diesel.
- At the high temperatures in engines, nitrogen from the air reacts with oxygen to form nitrogen oxides. These cause breathing problems and can cause acid rain.
- Burning fuels releases potentially harmful 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. This is thought to cause global warming.
- The pollution produced by burning fuels can be reduced by treating the combustion pollutants. This can remove substances like nitrogen oxides, sulfur dioxides and carbon monoxide.
- Sulfur can also be removed from fuels before we burn them to prevent forming sulfur dioxide.
- Some exhaust systems for vehicles are fitted with catalytic converters. These contain precious metals that once heated, cause the nitrogen oxides and carbon monoxides to produce nitrogen and carbon dioxides.
Advantages of Biofuels:
- Far less harmful to plants and animals than diesel from crude oils
- If spilled, breaks down 5 times faster than 'normal' diesel
- Burns cleaner, reduces the particulates emitted
- Produces very little sulfur dioxide
- As we run out of crude oils, biofuels will become cheaper in comparison
- The crops used to create biodiesel absorb CO2 as they grow, so its theoretically carbon neutral
- The solid waste can be used to feed cattle, and the glycerine can be used for making soap
Disadvantages of Biofuels:
- Farmland being used for fuel instead of food will impact the world's food supplies and may result in poorer countries experiencing famine
- Forests that absorb lots of carbon dioxide may be cleared to grow more biofuel crops
- Habitats of endangered species could be destroyed
- At low temperatures biofuels will start to freeze and turns into sludge.
- At high temperatures biofuels can tun sticky and 'gum up' engines.
- Ethanol can be made from fermenting the sugar from sugar beet or sugar cane.
- Some people add ethanol to our petrols to save crude oil.
- Ethanol may give off carbon dioxide, but sugar cane absorbs it during photosynthesis.
- Hydrogen burns cleanly and its only product is water.
- Water is a potentially enormous natural source of hydrogen, and electrolysis can be used to displace the hydrogen.
- We can split large hydrocarbon molecules up into smaller ones by: Mixing them with steam and heating them to a high temperature / By passing the vapours over a hot catalyst (porcelain chips).
- Cracking produces saturated hydrocarbons (alkanes) which are used as fuels, and unsaturated hydrocarbons (called alkenes), which have double carbon bonds.
- Alkanes do not react with orange bromine water, and it will stay orange.
- Alkenes react with orange bromine water, turning it colourless.
The general formula for alkenes:
- The chemicals we gain from crude oil are crucial, as we use them to make plastics.
- Plastics are made up of small molecules called monomers, which join up into huge molecules called polymers. We make them from ALKENES.
- These large polymers are made when small, reactive monomers join together.
- The reaction of making a polymer is called polymerisation.
- When ALKENE molecules join together, the double bond between the carbon atoms in each molecule 'opens up', and is replaced by single bonds as thousands of these molecules join together.
- New polymers are being developed all the time. They are designed to have properties that make them specialy suited for certain uses, e.g. new softer linings for dentures (false teeth), new packaging material, light sensitive plasters and implants that can slowly release drugs into a patient.
- Smart polymers may have their properties changed by light, temperature, or by other changes in their environment.
- Hydrogels are polymers chains with a few cross-linking units between chains, making a matrix that can trap water. These are perfect for wound dressings, as they allow the body to heal in moist, sterile conditions. As well as this, they can be used in contact lenses.
- To change the properties of hydrogels scientists just need to vary the amount of water in their matrix structure.
- PET plastic bottles can be recycled into polyester fibres for clothing; this is just one example of new uses we are finding for recycled plastics.
- Non-biodegrable plastics cause unsightly rubbish, can harm wildlife and take up unnecessary space in landfill sites.
- Biodegradable plastics are decomposed by the action of microorganisms in soil.
- Making plastics with starch granules in their structure helps the microorganisms break down a plastic.
- We can make biodegradable plastics from plant material such as cornstarch (PLA).
- Disadvantages of these biodegradable plastics include: farmers selling their crop for fuel rather than food, causing food prices to rise, possibly famine in poorer countries; destruction of habitats of wildlife; could affect global warming.
- Ethanol is an alcohol, so is in the -OH group. It is often written as C2H5OH.
- Ethanol is made by the fermentation of sugar from plants. Enzymes in yeast break down the sugar into ethanol and carbon dioxide gas.
- Mixing glucose solution and yeast and bubbling the gases produced through limewater will show if carbon dioxide is being given off. Then, by distilling the water and ethanol left over, you can collect the ethanol and it will burn with a 'clear' blue flame.
- Ethanol can be made from ethene reacting with steam in the presence of a catalyst. This is called hydration. The process is both continuous, and a reversible reaction. However, it is being completed with a non-renewable resource.
- Ethanol can be used as a solvent as it is highly volatile.
- Vegetable oils can be extracted from plants, by either crushing and pressing seeds, or by distillation of plants, which are boiled in water and the oil and water vapor are collected and condensed to be purified.
- Vegetable oils provide nutrients and have a high energy content. They are important foods and can be used to make biofuels.
- Unsaturated oils contain carbons with double bonds (C=C). We can detect them as double bond carbons decolourise orange bromine water.
- Boiling points of vegetable oils are much higher than that of water, meaning we can cook at higher temperatures and faster, the outsides of the food become crispier and insides softer.
- The food does absorb some of the oil, which increases the energy content of the foods compared to cooking in water.
- Vegetable oils are hardened by reacting them with hydrogen to increase their melting points. This makes them solids at room temperature, wihich are suitable for spreading. These are sometimes referred to as hydrogenated oils.
- The hardening reaction takes place at 60 degrees C with a nickel catalyst. The hydrogen adds onto C=C bonds in the vegetable oil molecules.
- Oils don't dissolve in water, but they can be dispersed (spread out) in each other to produce emulsions which have special properties, e.g. milk, which is animal fat dispersed in water.
- Emulsifiers are substances that stop oils and water from separating out into layers. This makes the emulusions thick and smooth for a long time.
- Emulsifiers are used in cosmetics like lipstick, face creams and body lotions, as well as foods like mayonnaise and ice cream.
How emulsifiers work:
- An emulsifier is a molecule with a 'tail' that is attracted to oil (hydrophobic) and a 'head' that is attracted to water (hydrophillic).
- The 'tail' is made of a long hydrocarbon chain, whereas the 'head' is a group of atoms that carry a negative charge.
- The 'tail' dissolves in the oil, forming oil droplets covered in the negative 'head's. As same charges repel, the oil droplets repel each other and keeps them spread out throughout the water.
- Substances that're added to foods to preserve it or improve its taste, texture, or appearance are called food additives. Approved additives for Europe are given E numbers. These can be used to identify which specific food additive has been used.
- Emulsifiers make oil and fat more edible in foods.
- Vegetable oils are high in energy content and provide nutrients. They are unsaturated and believed to be better for your health than saturated animal fats and hydrogenated vegetable oils. This is because you're less likely to take in all the energy content as their bonds are stronger.
The Earth consists of several layers:
- These start at the surface with the Earth's crust.
- Next is the mantle.
- Then there is an outer core...
- ... Followed by an inner core at the centre.
- A thin layer of gases called the atmosphere surrounds the Earth.
- The Earth's limited resources comes from its crust, the oceans and the atmosphere.
- The Earth's crust and upper mantle is cracked into a number of massive pieces, known best as tectonic plates. These are constantly moving, but only very slowly.
- The motion of the tectonic plates is caused by convection currents in the mantle, due to radioactive decay which heats molten minerals that rise till they cool, then sink again.
- Earthquakes and volcanoes happen when tectonic plates meet. It's difficult to know when the plates may slip past each other, which makes it difficult to accurately predict earthquakes.
- Scientists think the Earth was formed about 4.5 billion years ago, as a molten ball of rock and minerals. For its first billon years it was a very violent place, with volcanoes throwing fire and gases into the atmosphere.
- One theory about the Earth's early atmosphere is that volcanoes released carbon dioxide, water vapor and nitrogen gas, which formed the early atmosphere.
- The water vapour in the atomosphere condensed as the Earth gradually cooled down, and fell as rain. Water collected in hollows in the crust as the rock solidified, and the first oceans were formed.
- As Earth began to stabilise, the atomosphere was probably made up mostly of carbon dioxide, with traces of methane and ammonia along with the remaining water vapour. This means there would be very little oxygen if any at all.
- Scientists believe simple organisms similar to bacteria appeared about 3.4 billion years ago, making food for themselves from chemical breakdowns. Then bacteria and algae evolved, which would've started to photosynthesise and produce oxygen as a waste product.
- By 2 billion years ago, more plants were evolving and raising oxygen levels. This meant animals could evolve, but they couldn't make their own food and needed oxygen to respire.
- 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 remain unproven. We simply cannot be sure about the events that resulted in the first life-forms on Earth as no one was there to document it, and several experiments have brought similar results.
- The main gases in the Earth's atmosphere are oxygen and nitrogen.
- About four-fifths (78%) of the atmosphere is nitrogen, 21% is oxygen, and the rest are things such as carbon dioxide, argon and other trace elements.
- The main gases in the air can be separated by fractional distillation. These gases are used in industry as useful raw materials.
- Carbon moves into and out of the atmosphere due to plants, animals, the oceans and rocks. This is known as the carbon cycle.
- The amount of carbon dioxide in the Earth's atmosphere has risen in the recent past. This is largely due to the amount of fossil fuels we now burn.