Chemistry unit 1

All substances are made up of atoms. Elements contain only one type of atom. Different atoms can bond together by giving, taking or sharing electrons, to form compounds.

Limestone is made mainly of calcium carbonate. Limestone is widely used in building. Limestone breaks down when we heat it strongly (thermal decomposition) to make quicklime and carbon dioxide.

 Some carbonates decompose when we heat them in a bunsen flame. There is the same number of each type if atom on each side of a balanced chemical equation. The mass of reactants is the same as the mass of the products in a chemical reaction.

When water is added to quicklimke it produces slaked lime. Lime mortar is made by mixing slaked lime with sand and adding water.

Cement is made by heating powdered limestone with clay in a kiln. Concrete is made by mixing crushed rocks, cement and sand with water. Glass is made by heating powdered limestone, sand and sodium carbonate together very strongly.

The earths crust contains many different elements. A metal ore contains enough of the metal to make it economically worth extracting the metal. We can find gold and other unreactive metals in their native state. The reactivity series is useful in deciding the best way to extract a metal from its ore. Metals more reactive than carbon cannot be extracted from their ores using carbon.

We extract iron from iron ore by reducing it with carbon in a blast furnace. The solid raw materials used to make iron are iron ore (haematiite), coke and limestone. Molten iron is tapped from the bottom of the blast furnace.

Pure iron is too soft for it to be very useful. Carefully controlled quantities of elements are added to iron to make alloys of steel with different properties.

Copper, gold and aluminium are all alloyed with other metals to make them more useful. We can control the properties of alloys bu adding different amounts of different elements. Smart alloys are also called memory alloys, when deformed they return to their original shape on heating. Shape memory alloys can be used in medicine and dentistry

The transition metals are found in the middle block of the periodic table. Transition metals have properties that make them useful for building and making things. Copper is a very useful transition metal because of its high conductivity.

Aluminium and titanium are useful because they resist corrosion. Aluminium and titanium are expensive because extracting them from their ores involves many stages in the processes and requires large amounts of energy. Recycling aluminium is important because we need to use much less energy to produce 1kg of recycled aluminium than we need to extract 1kg of aluminium from its ore.

Crude oil is a mixture of many different compounds. Many of the compounds in the crude oil are hydrocarbons - they contain only carbon and hydrogen. Alkenes are saturated, they contain as much hydrogen as possible in theit molecules.

We seperate crude oil into fractions using fractional distilation. Properties of each fraction depend on the size of the hydrocarbon molecules. Lighter fractions make better fuels.

When we burn hydrocarbon fuels in plenty of air they produce carbon dioxide and water. Impurities in fuels may produce other substances which may be poisonous and/or which may cause pollution. Changing the conditions in which we burn fuels mau change the products that are made.

Burning fuels releases substances that are spread throughout the atmosphere. Some of these substances dissolve in droplets of water in the air, which then fall as acid rain. Carbon dioxide producedfrom buring fuels is a greenhouse gas, it reduces the rate at which energy is lost fron the surface of the Earth by radiaiton. The pollution produced bu burning fuels may be reduced by treating the products of combustion, this can remove substances like nitrogen oxide, sulfur dioxide and carbon monoxide.

We can split large hydrocarbon molecules up into smaller molecules by heating them and passing the gas over a catalyst. Cracking produces unsaturated hydrocarbons we call alkenes. Alkenes burn, and also react with bromine water, producing colourless products.

Plastics are made from polymers. Polymers are large molecules made when monomers (small molecules) join together.

Monomers affect the properties of the polymers that they produce.Changing reaction conditions can also change the type of polymer that is produced.

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.

Vegetable oils can be extracted from plants by pressing or by distilation. Vegetable oils are important foods. Unsaturated oils contain carbon-carbon double bonds. We can detect them using bromine or iodine solutions.

Vegetable oils are useful in cooking because of their high boiling points. Vegetable oils are hardened by reacting them with hydrogen to increase their boiling and melting points.

Oils do not dissolve in water. Oils can be used to produce emulsions which have special properties. Emulsions made from vegetable oils are used in many foods, such as salad dressings and ice creams.

Additives may be added to food in order to improce its appearance, taste and how long it will keep (its shelf-life). Food scientist can analyse foods to identify additives.

Vegetable oils can be burned as fuels. Vegetable oils are a renewable source of energy that could be used to replace some fossil fuels.

The earth consists of a series of layers. Scientist originallly thought that the features on the Earth's surface were caused as the crust cooled and shrank.

The Earth's listmosphere is cracked into a number of pieces (tectonic plates) which are constantly moving. The motion of the tectonic plates is caused by convection currents in the mantle, due to radioactive decay. Earthquakes and volcanoeshappen where tectonic plates meet. It is difficult to know when the plates may slip past eachother. This makes it difficult to predict  accurately when and where earthquakes will happen.

The Earth's early atmosphere was formed by volcanic activity. It probably consisted mainly of carbon dioxide. There may also have been water vapour toghether with traces of methane and ammonia. As plants colonised the Earth, the level of oxygen in the atmosphere rose.

The main gases in the Earth's atmosphere are nitrogen and oxygen. About four-fifths (80%) of the atmosphere is nitrogen, and one-fifth (20%) is oxygen. The noble gases are unreactive gases found in Group 0 of the periodic table. Their lack of reactivity makes them useful in many ways.

Carbon moves into and out of the atmosphere due to plants, the oceans and rocks. The amount of carbon dioxide in the Earth's atmosphere has risen due to the amount of fossil fuels we burn.