chemistry

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  • Created by: Sophiw
  • Created on: 15-12-12 14:38

atomic structure

  • all matter is made from atoms they cannot be made or destroyed 
  • in the middle on an atom there is a nucleus with electrons orbiting in fixed shells around it
  • nucleus is made up of two subatomic particles called protons which are positively charged and neutrons which have no electrical charge - electrons are negatively charged, thus an atom overall is neutral 
  • the atomic number is the bottom number which displays the number of protons it contains whilst the mass number is the top number and displays the total number of protons and neutrons 
  • isotopes are varieties of an element that have the same atomic number but different mass numbers
  • when an atom becomes a ion its nucleus stays the same but it either looses an electron making it positively charged or gains ones making it negatively charged 
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electronic structure

  • compounds are substances that contain two or more different elements chemically combined 
  • at first scientists thought that atoms were positively charged which electrons dotted about inside, to develop this idea positively charged particles were fired at gold atoms, instead of going straight through like they thought they would they were deflected
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ionic bonding

  • hydrogen and metal atoms usually form positively charged ions wheras non metal atoms usually form negatively charged ions
  • the formulae for ions contain either a + or - to highlight if they are positively or negatively charged
  • in ionic bonding a metal reacts with a non metal and electrons are transferred from the metal atoms to the non metal atoms; this is because metals are positive and non metals are negative and thus they attract each other and form an ionic bond
  • in ionic bonding diagrams different atoms are shown by either dots or crosses and after being ionised two lines appear either side with a - or + to show its new found charge
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ionic compounds

  • magnesium oxide and sodium chloride are examples or ionic compounds, they both have high melting points, but sodium chloride dissolves in in water whereas magnesium oxide does not
  • they both do not conduct electricity when they are solid, however when they are molten they can but their high melting points make this difficult to occur , however when sodium chloride dissolves in water the solution can conduct electricity
  • the way ionic compounds are arranged is called a giant ionic lattice, the word giant displays the structure is repeated many times and the positive and negative ions are very strongly attached
  • ionic bonds are strong chemical bonds and a lot of energy is needed to break them this is why they have high melting points, for them to conduct electricity the electrons must be free to flow this can happen in a liquid but not a solid
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electrons and the periodic table

  • horizontal row of elements is called a period, which is displays the number of shells
  • vertical column is a group, in each group they all have similar chemical proporties, the group also displays the number of electrons on the last shell
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covalent bonding

  • non metals combine with eachother to form covalent compounds, instead of ionic bonding they have covalent bonding in which there is a shared paid of electrons
  • when drawing a molecule or covalent bonding only the outer shell needs to be shown, again crosses and dots represent different molecules
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group 1 elements

  • they are all metals and react vigorously with water to form alkaline solutions so they are alkali metals
  • lithium, potassium and sodium are examples, they react so badly with air and water they must be stored under oil
  • metal + water -> metal hydroxide + hydrogen
  • 2M + 2H20 -> 2MOH + H2
  • when in water potassium floats, melts to form a silvery ball and then ignites explosively and burns with a lilac flame and disappears very quickly
  • sodium floats and forms a silvery ball and dissapears quickly
  • lithium floats and keeps it shape and dissapears slowly
  • the easier it is to lose an electron the more reactive it is, the loss of electrons is called oxidation
  • oxidation of metal = M -> M+ + e-
  • density, reactiveness and melting points increase the further you go down
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flame tests

  • high temperatures added to metal compounds vaporise the metal ions, they absorb heat energy and cause electrons to jump to higher shells , when they drop back to their normal shells light energy is released
  • potassium produces a blue flame, sodium orange and lithium red 
  • to carry out a flame test a flame test wire made out of a loop of nichrome alloy wire which is cleaned by adding it either into nitric or hydrochloric acid , then held over the blue flame
  • the loop is added to acid to moisten it then into the metal compounds it is held at the edge of the blue flame and the colour is observed
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group 7 elements

  • group 7 elements are called halogens because they react with metals to form salt
  • chlorine sterilises tap water and swimming pools as it kills the harmful bacteria, it can also be used to make pesticides and plastics such as pvc also iodine is used as an antiseptic to sterilise wounds
  • group 7 elements are coloured and they occur at different states at room temperature: chlorine is a green gas, bromine is an orange liquid and iodine is a grey solid but when iodine is warmed it can easily change to a purple vapour
  • it is possible to predict the physical properties using the properties of the other elements in the group as their melting and boiling points change in a regular way
  • group 7 elements react vigorously with group 1 elements especially is the metal is heated, metalhalide is then produced
  • group 1 with group 7: 2M + X2 -> 2MX
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displacement reactions

  • group 7 elements can react with metal halides, the group 7 elements displace the halogen from the solution, this is called a displacement reaction
  • a more reactive group 7 element will displace a less reactive group 7 element from the metal halide
  • most reactive elements are at the top of the group 7 elements but the opposite for group 1
  • displacement reaction MY( metal halid ): X2 + 2MY -> Y2 + 2MX
  • in group 7 the gain of an electron makes it a noble gas and this is called reduction : X2 + 2e- -> 2X-
  • it is easier for the group 7 element to gain an electron the more reactive it is
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the transition elements

  • transition elements are all metals with typical metal proporties such as they are shiny when cut, strong and malleable ( can be hammered into shape )
  • copper compounds such as copper sulfate solutions are blue, iron II compounds such as iron II sulfate solution is light green and iron III compounds such as iron III chloride solution is orange-brown
  • they transition elements and their compounds can often be used at catalysts, iron is the catalyst used to increase the rate of reaction between nitrogen and hyrdogen in the haber process
  • some carbonates of the transition metals can cause a thermal decomposition reaction: metal carbonate -> metal oxide + carbon dioxide
  • a colour change is usually seen in the reaction and carbon dioxide can be detected using the limewater test
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precipitation reactions

  • precipitation reactions happen when a mixture of solutions react to make an insoluble solid called the precipitate, this makes the solution cloudy and different metal ions give different colours and thus is how the transition metal ions can be identified
  • when the transition element is dissolved in water the metal ions separate out then thet react with the hydroxide ions to form the metal hydroxide precipitates
  • copper II makes blue, iron II makes grey-green and iron III makes orange-brown
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metallic structure

  • copper is a good conductor of electricity and makes brass and electrical wiring, iron is used to make steel and used to make cars and bridges because it is strong
  • metals are hard, shiny, good conductors of heat and electricity and have a high tensile strength so they resist being stretched, they also have high melting and boiling points
  • metals are held together by metallic bonds which are very strong
  • metals contain positive metal ions packed closely, these form when the electrons leave the outer shell and becaome free to move within the structure of the atoms creating a sea of delocalised electrons
  • metallic bonding is due to the strong force of attraction betwenn the sea the closely packed positive metal ions, the forces are very strong and a lot of energy is needed to overcome them
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superconductors

  • metal structures contain crystals because the particles are packed closely in regular arrangemment and is repeated producing crystals
  • the metal crystals contain delocalised electrons, as they are free flowing they are why metals can conduct electricity however the path is not clear and thus causes electrical resistance, which makes metals heat up when they conduct electricity wasting energy
  • the resistance of metals decrease as the temperature does, thus some metals become superconductors, they can make electromagnets and mri scanners
  • superconductors could also be used to make super fast electronic circuits leading to extremely powerful computers, they could also replace traditional metal cables, and little loss of energy would occur as they is not alot of no resistance
  • at the moment superconductors only work at very low temperatures, which means the applications are limited
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purifying water

  • water is an important resource for many industrial chemical processes as it may be used as solvents to dissolve other substances, coolants to stop overheating happening or a cheap raw material
  • common pollutants of water include, nitrates from eutrophication, lead compounds from old lead pipes and pesticides from spraying crops
  • water has to be purified before it can be used, large suspended particles are removed through sedimentation then filtration removes small suspended particles then chlorine gas is added to kill microbes in the water this process is called chlorination
  • very pure water can be produced from the sea by distillation but it uses a lot of energy and it is very expensive to make large amounts
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testing water

  • barium chloride solution is used to test for dissolved sulfate ions, a white precipitation forms if sulfate ions are present: sodium sulfate + barium chloride -> sodium chloride + barium sulfate ( white precipitation )
  • silver nitrate is used to test for dissolved halide ions: chloride ions make a white precipitate, bromide ions produce a cream precipitate and iodine ions produce a pale yellow precipitate: sodium chloride + silver nitrate -> sodium nitrate + silver chloride ( white precipitation )
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