Chemistry c1

1. substances

   Annotations:

   • All substances are made of atoms. A substance that is made of only one sort of atom is called an element. There are about 100 different elements. Elements are shown in the periodic table. The groups contain elements with similar properties.
2. symbols

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   • Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, and Na represents an atom of sodium.
3. structure

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   • Atoms have a small central nucleus, which is made up of protons and neutrons and around which there are electrons. 
4. charges

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   • The relative electrical charges are as shown: Name of particle Charge Proton                     +1 Neutron                    0 Electron                   –1
5. electrons

   Annotations:

   • In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge. 
6. protons

   Annotations:

   • All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons. 
7. atomic number

   Annotations:

   • 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.
8. energy levels

   Annotations:

   • Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells). 

1. groups and properties

   Annotations:

   • Elements in the same group in the periodic table have the same number of electrons in their highest energy level (outer electrons) and this gives them similar chemical properties.
2. Nobel gases

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   • 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. 

1. Compounds

   Annotations:

   • 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. Compounds formed from non-metals consist of molecules. In molecules the atoms are held together by covalent bonds. 
2. Equations

   Annotations:

   • Chemical reactions can be represented by word equations or by symbol equations.
3. Balancing equations

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   • No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.

1. Limestone

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   • Limestone, mainly composed of the compound calcium carbonate (CaCO3 ), is quarried and can be used as a building material.
2. Decomposition

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   • Calcium carbonate can be decomposed by heating (thermal decomposition) to make calcium oxide and carbon dioxide.
   1. carbonates

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      • The carbonates of magnesium, copper, zinc, calcium and sodium decompose on heating in a similar way
3. Calcium Oxide

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   • Calcium oxide reacts with water to produce calcium hydroxide, which is an alkali that can be used in the neutralisation of acids.
4. Solutions

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   • A solution of calcium hydroxide 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
5. Acid Rain

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   • Carbonates react with acids to produce carbon dioxide, a salt and water. Limestone is damaged by acid rain.
6. Cement

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   • Limestone is heated with clay to make cement. Cement is mixed with sand to make mortar and with sand and aggregate to make concrete.

1. Economical

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   • Ores contain enough metal to make it economical to extract the metal. The economics of extraction may change over time
2. purification

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   • Ores are mined and may be concentrated before the metal is extracted and purified
3. Unreactive metals

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   • 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 to extract the metal.
4. Metals that are less reactive than carbon

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   • Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon, for example iron oxide is reduced in the blast furnace to make iron. 
5. Metals that are more reactive than carbon

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   • Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive.  
6. Copper

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   • 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. 
   1. low grade copper extraction

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      • 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. 
   2. electrolysis/ displacement

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      • Copper can be obtained from solutions of copper salts by electrolysis or by displacement using scrap iron.
7. Aluminium & titanium

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   • 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 processes ■ large amounts of energy are needed. 
8. Recycling

   Annotations:

   • We should recycle metals because extracting them uses limited resources and is expensive in terms of energy and effects on the environment.

1. Iron
   1. uses

      Annotations:

      •  Iron from the blast furnace contains about 96% iron. The impurities make it brittle and so it has limited uses
   2. Steels

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      • Most iron is converted into steels. Steels are alloys since they are mixtures 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. 
2. Most metals

   Annotations:

   • 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

1. Transition Metals

   Annotations:

   • 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.
2. Copper

   Annotations:

   • Copper has properties that make it useful for electrical wiring and plumbing.  
3. aluminium and Titanium

   Annotations:

   • Low density and resistance to corrosion make aluminium and titanium useful metals. 

Annotations:

• Crude oil is a mixture of a very large number of compounds.

1. Mixture

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   • A mixture consists of two or more elements or 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.
2. Compounds in crude oil

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   • 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, 
3. General formula

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   • Alkanes: CnH2n+2.

1. Alkanes

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   • Alkane molecules can be represented in the following forms: ■ C2H6                H       H                       I         I■ H –– C –– C –– H                            I         I                              H      H
2. Fractional distillation

   Annotations:

   • 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
3. Properties

   Annotations:

   • Some properties of hydrocarbons depend on the size of their molecules. These properties influence how hydrocarbons are used as fuels.

1. Releases

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   • 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
2. Oxidation
3. Sulphur dioxide
   1. Global dimmming

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      • Sulfur dioxide and oxides of nitrogen cause acid rain, carbon dioxide causes global warming, and solid particles cause global dimming
   2. removal of sulphur

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      • Sulfur can be removed from fuels before they are burned, for example in vehicles. Sulfur dioxide can be removed from the waste gases after combustion, for example in power stations. 
4. Biofuel

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   • Biofuels, including biodiesel and ethanol, are produced from plant material. There are economic, ethical and environmental issues surrounding their use.