Chemistry GCSE Unit 3 Mindmap PART 1

Taken from AQA GCSE textbook!

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  • Created by: A.B.
  • Created on: 09-04-13 14:32
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  • Chemistry Unit  3 Part 1
    • The Periodic Table
      • The Early Periodic Table
        • The periodic table of elements developed as chemists tried to classify the elements. It arranges them in a pattern in which similar elements are grouped together.
          • Periodic means regularly occuring.
        • Newlands' table put the elements in order of atomic mass but failed to take account of elements that were unknown at the time.
          • 1864, Built on John Dalton's work who had arranged elements using the 'law of octaves' however some elements did not fit the pattern.
        • Mendeleev's periodic table left gaps for the unknown elements, and so provided the basis for the modern periodic table.
          • 1869, around 50 elements had been discovered and were arranged in order of atomic weights.
      • The Modern Periodic Table
        • The atomic (proton) number determines the element's position on the periodic table.
          • Not all elements fit the pattern e.g. argon when arranged by atomic masses  (Mendeleev).
          • At the start of the 20th century
        • The number of electrons in the outermost shell (highest energy level) determines its chemical properties.
        • The group number in the periodic table equals the number of electrons in the outer shell.
          • The periodic table is arranged with reactive metals in groups 1 and 2, non-metals groups 3 to 7 (with some omitted  to the left of  the diagonal line, noble gasses (very unreactive) and transition metals in the centre.
        • We can explain trends in the reactivity as we go down a group in terms of: the distance between the outermost electrons and the nucleus and the number off occupied inner shells (energy levels) in the atoms.
          • For group 1, the reactivity increases going down the group because, to react, the element has to lose the 1 electron so it needs as little attraction as possible between the outer electron and the nucleus.
          • For group 7 the reactivity decreases going down the group because, to react, the element has to gain 1 electron so it needs as much energy as possible between the outer shell and the nucleus.
      • Group 1 - The Alkali Metals
        • The elements in Group 1 of the periodic table are called the alkali metals.
          • The metals in this group are: lithium, sodium, potassium, rubidium, caesium and francium.
        • Their melting and boiling points decrease going down the group.
          • The atoms get heavier as they move down the group.
        • The metals all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide.
          • They also have very low densities and are very soft. They have a silvery surface which reacts with oxygen and goes dull (forms a layer of oxide).
          • Floats on water and fizzes.
        • They form 1+ ions in reactions to make ionic compounds, These are generally white  and dissolve in water, giving colourless solutions.
        • The reactivity of the alkali metals increases going down the group.
      • The Transition Elements
        • Compared with the alkali metals, transition elements have much higher melting points and densities. They are also stronger and harder, but are much less reactive.
          • Have the properties of 'typical' metals.
        • The transition elements do not react vigorously with oxygen or water.
          • If they corrode, they do so very slowly.
            • Compared with the alkali metals, transition elements have much higher melting points and densities. They are also stronger and harder, but are much less reactive.
              • Have the properties of 'typical' metals.
            • Makes them useful as structural materials.
        • A transition element can form ions with different charges, in compounds that are often coloured.
          • The roman numeral shows the charge.
        • Transition elements and their compounds are important industrial catalysts.
          • For example, it is possible to use nickel as a catalyst for the manufacture of margarine.
      • Group 7 - The Halogens
        • The halogens all form ions with a single negative charge in their ionic compounds with metals.
        • The halogens form covalent compounds by sharing electrons with other non-metals.
          • In element form, they are in pairs.
          • Take part in both ionic and covalent bonding.
        • A more reactive halogen can displace a less reactive halogen from a solution of one of its salts.
          • Fluorine displaces all others as it is most reactive, however it reacts so strongly with water that it is impossible to carry out reactions in aqueous solutions.
        • The reactivity of the halogens decreases going down the group.
        • The halogens are poisenous non-metals that form coloured vapours.
        • Have low melting and boiling points and are poor conductors of energy and electricity.
          • They are relatively heavy.
    • Water
      • Hard Water
        • Hard water contains dissolved compounds such as calcium and magnesium salts.
          • Dissolve when the water flows over rocks containing the compounds. Acid rain (dissolved carbon dioxide) causes calcium carbonate (limestone) to dissolve into the water.
            • The dissovled calcium carbonate reacts with the weak acidity and forms hydrocarbonate which is soluble in water and makes it hard.
        • The calcium  and/or magnesium ions in hard water react with soap producing a precipitate called scum.
          • Soapless detergents do not produce scum.
          • soap stearate + calcium ions -> calcium stearate precipitate (scum) + sodium ions (soluble).
          • Adds expense as soap is wasted.
        • One type of hard water can produce a solid scale when it is heated, reducing the efficiency of heating systems and kettles.
        • Hard water is better than soft water for developing and maintaining teeth and bones. It may also help prevent heart disease.
        • Difficult to produce a soapy lather.
      • Removing Hardness
        • Soft water does not contain ions that produce scum or scale.
        • Hard water can be softened by removing the ions that produce scum and scale.
          • Don't waste soap or get scum or scale formed. Possibly worse for health if softened.
        • Temporary hardness is removed from water by heating it. Permanent hardness is not changed by heating.
          • This produces scale (the calcium and magnesium ions in the form of a precipitate) causing it  to go soft.
            • The hydrogencarbonate ions in temporary hard water decompose on heating. The carbonate ions formed react with calcium and magnesium ions, making precipitates.
          • This is an expensive process and can waste energy.
        • The hydrogencarbonate ions in temporary hard water decompose on heating. The carbonate ions formed react with calcium and magnesium ions, making precipitates.
        • Either type of hard water can be softened by adding washing soda or by using an ion-exchange resin to remove calcium and magnesium ions.
          • Sodium carbonate is washing soda. The ions from sodium carbonate react with the hardness and cause it to produce calcium carbonate which precipitates out.
            • Similar to the formation of scale except it does not waste energy and it happens more quickly.
          • The column is usually packed with a resin containing sodium ions which are exchanged for calcium and magnesium ions. The resin can be recharged by washing it in salt.
      • Water Treatment
        • Water for drinking should contain only low levels of dissolved substances and microbes.
          • Home filters contain carbon to reduce the levels of chlorine and pesticides. It also contains ion exchange resin to remove calcium, magnesium, lead, copper and aluminium ions. Silver particles discourage the growth of bacteria.
        • Water is made fit to drink by filtering it to remove solids and adding chlorine to reduce the number of microbes.
          • Passes through 5 stages: Settling soil out, aluminum sulfate and lime added to clump dirt, fine sand filter, chlorine added and pH checked.
        • We can make pure water by distillation but this requires large amounts of energy which makes it expensive.
          • Evaporated then condensed.
        • Water is used as a raw material, a solvent, a coolant, for washing and drinking.
      • Water Issues
        • Chlorine is added to water to sterilise it by killing microbes.
          • Although it is poisonous, many people believe the benefits outweigh the risks however ozone can be used as an alternative.
        • Fluoride helps to improve dental health.
          • Can cause fluorosis which weakens bones. Benefit is not significant. Ethically wrong for choice to be made without consent. Some think it produces learning disabilities and alzheimer's disease.
          • 50 years - only noticed fluorosis. 30% reduction in teeth cavities. Protect those who do not have good dental hygiene. Bacteria related to tooth decay can cause heart disease. Only added in tiny parts (1ppm).
        • Some argue against the fluoridation of public water supplies. For example, they think that people should have the right to choose if they want to take extra fluoride or not.
    • Energy Calculations
      • Comparing the Energy Released by Fuels
        • When fuels and food react with oxygen, energy is released in an exothermic reaction.
        • A simple calorimeter can be used to compare the energy released by different fuels or different foods in a school chemistry lab.
          • The equation used to find the energy released is: energy released = mass of water heated (g) x specific heat capacity of water (usually 4.2) x rise in temperature (degrees C).
          • Can be found per gram or per mole (use relative formula mass (mr).
            • Have to know how much mass decreases by to know how much is burned.
      • Energy Transfers in Solutions
        • We can calculate the energy change for reactions in solution by measuring the temperature change and using the equation: Q = mcdT
          • The equation used to find the energy released is: energy released = mass of water heated (g) x specific heat capacity of water (usually 4.2) x rise in temperature (degrees C).
          • Calculate the temperature change then the energy change. Possible to work out per mole.
          • Useful when solutions are mixed and there is a temperature change.
            • Neutralisation and displacement reactions are both examples of reactions we can use this technique for.
        • Neutralisation and displacement reactions are both examples of reactions we can use this technique for.
      • Energy Level Diagrams
        • We can show the relative difference in the energy of reactions and products on energy level diagrams.
          • Energy is measured in kJ/mol
          • For exothermic reactions, energy is released therefore on an el diagram, the products are shown at a lower energy level than the reactions.
            • Opposite for endothermic
              • Untitled
        • Catalysts lower the activation energy so a greater proportion of reactant particles have enough energy to react.
          • The activation energy is the lowest amount of energy needed to start the reaction.
        • Bond breaking is endothermic and bond making is exothermic.
          • Bonds are both made and broken during a reaction. It depends which involves the most energy to what the reaction is overall.
      • Calculations Using Bond Energies
        • In chemical reactions, energy must be supplied to break the bonds between atoms in the reactants.
        • When new bonds are formed between atoms in a chemical reaction, energy is released.
        • In an exothermic reaction, the energy released when new bonds are formed is greater than the energy absorbed when bonds are broken.
        • In an endothermic reaction, the energy released when new bonds are formed is less than the energy absorbed when bonds are broken.
        • We can calculate the overall energy change in a chemical reaction using bond energies.
          • Use bond energies to calculate how much energy is gained/lost on each side to work out the overall energy change.
      • Fuel Issues
        • Much of the world relies on fossil fuels. However they are non-renewable and they cause pollution. Alternative fuels need to be found soon.
        • Hydrogen is one alternative. It can be burned in combustion engines or used in fuel cells to power vehicles.
          • Hydrogen + oxygen -> water.

Comments

MagicMuffins

Great amount of detail. Have you taken this out of the student text book by any chance?

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