Chemistry

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  • Created by: AOconnor
  • Created on: 13-05-18 13:32
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  • Chemistry
    • Separating Mixtures
      • Filtration separates soluble solids from insoluble solids by dissolving and filtering
      • Crystallisation obtains a soluble solid from a solution
        • Mixture is warmed then water evaporates, leaving solid
      • Distillation obtains solvent from solution via evaporation and condensation
      • Fractional distillation separates mixtures containing components with different boiling points
      • Chromatography separates the different soluble coloured components of a mixture
    • Periodic Table
      • Development
        • Newlands arranged via atomic weight, so some were in the wrong place
        • Mendeleev left gaps to allow discovery
          • Organised via increaseing atomic number
          • Each element was in a group with others that had similar properties
      • Group 0 (Noble gases)
        • Full outer shell making them unreactive
      • Group 1 (Alkali Metals)
        • Low melting/boiling point that decrease down group
        • Reactivity increases down group as electron can be lost more easily
          • React vigorously so kept in oil
          • When reacting with water, metal hydroxide is formed and hydrogen released
            • When hydroxide dissolves, alkaline solution produced
        • Low density (float on water)
      • Group 7 (Halogens)
        • Reactivity increases down group (harder to gain electron)
          • React with metals to produce ionic salts
          • More reactive halogens displace less reactive ones
    • Atoms
      • Isotopes have the same number of protons but different neutrons
      • Ions form when an atom loses/gains electrons
      • Plum Pudding
        • Atoms contained tiny, negative electrons surrounded by sea of positive charge
        • Disproved when scientists fired alpha particles at sheet of gold
          • Most passed through but some deflected back
            • Meant that the positive charge was concentrated in a small area
    • Ionic compounds
      • Transfer of electrons from metal to non-metal
      • Ionic bond is strong electrostatic attraction between positive and negative ions
      • Properies
        • High melting/boiling point (ionic bonds are hard to overcome)
        • Only conduct electricity when aqueous or molten
    • Covalent Compounds
      • Shared pair of electrons between atoms (2 non-metal)
      • Strong covalent bonds
      • Small molecules
        • Small number of atoms joined via covalent bond
        • Weak intermolecular forces (low melting point)
          • Larger the molecule, stronger the intermolecular forces
      • Giant structures
        • Strong covalent bonds (high melting point)
        • Diamond
          • Giant rigid structure (lattice)
            • 1 carbon joins 4 other carbons)
            • Strong bonds means high melting point
            • No charged particles so doesn't conduct electricity
        • Graphite
          • High melting point and giant lattice
            • 1 carbon joins 3 others (layered hexagonal structure)
              • Weak intermolecular forces between layers causes sliding
              • 1 electron is delocalised and can carry charge around structure
                • Conducts electricity
        • Silicon dioxide
          • Similar to diamond
            • 1 oxygen joined to 2 silicon
            • 1 silicon joined to 4 oxygen

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