C4 - Chemistry

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  • C4
    • Atomic Structure
      • Protons have a charge of +1, Neutrons 0 and Electrons -1
      • When looking at an element in the periodic table, the bigger top number is the relative atomic mass and the smaller bottom number is the atomic number
        • The atomic mass is protons + neutrons and the atomic number is both the number of protons and electrons
      • Some elements have two different atomic masses, yet the same atomic number. These are called isotopes
        • Example: Chlorine. 75% of chlorine atoms have 18 neutrons, 25% have 20, making the mass either 37 or 35.
      • Elements in the same group (vertical) have the same amount of electrons and elements in the same period (horizontal) have the same number of shells
    • Ionic Bonding
      • Ionic bonding happens between a metal and non-metal ion
        • Electrons transfer from the metal to the nonmetal, causing them to be attracted to eachother
          • These form giant ionic lattices, which have strong attractions, They are solid.
      • If an atom loses electrons it becomes positive and if it gains electrons it becomes negative
      • The 'Dot and Cross' model can describe ionic bonding
        • During the bonding of magnesium oxide: the magnesium atoms lose 2 electrons to form positive ions. The electrons go to the oxygen making it negative.
          • Magnesium has two electrons in its outer shell, whereas oxygen has 6. To make a full shell of 8, magnesium 'donates' its 2 to oxygen
    • The Periodic Table and Covalent Bonding
      • Covalent bonding is where non-metals combine with eachother, sharing electrons to form covalent compounds
      • 1865 > Newlands put 56 elements into groups and saw that every 8th element acted similarly
        • 1869 > Mendeleev arranged the elements in order in a table, noticing gaps and predicting new elements
    • Group 1 (Alkali Metals)
      • Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr)
        • Less dense  Most dense
          • High melting Low melting
      • Metal + Water > Metal hydroxide + hydrogen
      • All group 1 elements have 1 electron in their outer shell. The further down the table, the more shells, so the electron is further from the nucleus, so the bond is weaker and the element is more reactive
      • Flame Test: This tests for the presence of the less reactive group 1's. Simply hold a wet splint with the compound over a flame and observe the colour
        • Lithium is red, sodium is orange and potassium is purple.
    • Group 7 (Halogens)
      • Chlorine is a green gas used in pools, bromine is an orange liquid used in insecticides, iodine is a grey solid used as an antiseptic and flourine is a yellow gas added to toothpaste
      • They all have 7 electrons in their outer shells so share to make 8
      • When group 7 and group atoms react a metal halide is made
        • E.g. potassium + iodine > potassium iodide
          • In a symbol equation there is usually 2 halogens
      • If a halogen is are added to a less reactive metal halide solution, the halogen replaces the current one. This is displacement
        • E.g. flourine + sodium chloride > sodium flouride + chlorine
    • Transition Elements
      • These are inbetween groups 2 and 3. They often form coloured solutions/compounds
        • Copper  is blue, iron (11) is light green and iron (111) is orange
        • They often form catalysts. Iron speeds up ammonia and nickel speeds up margerine
      • In thermal decomposition, one substance breaks down to form 2 or more other substances
        • Metal carbonate > metal oxide + carbon dioxide
          • This is tested in the lime water test where water goes cloudy
    • Metals and Superconductors
      • Properties: copper can be used in saucepans due to its high conductivity of heat and aluminium is used in aircraft due to its low density
      • Metals have very strong bonds as they're shaped as regular lattice structures. The metal ions are closely packed with a sea of delocalised electrons inbetween
      • Superconductors are materials that conduct with little or no resistance, meaning they lose no energy
        • Advantages: loss free energy, environmentally efficient due to low CO2 emissions, smaller motors
        • Drawbacks: restricted range of temperatures, could be dangerous, brittle and sensitive
    • Purifying Water
      • Sources: rivers, lakes, ponds, wells, canals, streams, oceans
      • Used in the production of wood, paper, metals, oils, gasolines and chemicals
      • Substances like agricultural run off, sewage, phosphats, nitrates, salt and mercury get into water and must be removed
      • They are removed in 3 main stages
        • 1) Sedimentation, where chemicals make large particles settle at the bottom
          • 2) Filtration removes very fine particles in sand and gravel filter beds
            • Chlorination kills disease causing microbes




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