Unit 3 Chemistry

• Metallic bonding is the electrostatic attraction between positively charged ions and delocalized electrons
• In metallic lattices, electrons are delocalized, allowing for the conduction of electricity
• Metallic elements are conductors of electricity because they contain delocalized electrons
• When an isotope emits an alpha particle:

  • Atomic number decreases by two
  • Mass number decreases by four
• When an isotope emits a beta particle:

  • Atomic number increases by one
  • Mass number stays the same
• When an isotope emits gamma rays:

  • Atomic number and mass number stay the same
• In the decay sequence of polonium-218:

  • 218Po decays to 214Pb, which further decays to 214Bi
• Radioisotopes of iodine can be used in medicine to test thyroid function and iodine-131 is used in radiation therapy for thyroid cancer
• In industry, domestic smoke alarms use the alpha emitter americium-241 due to its low penetrating power and long half-life
• Half-life is the time for half of the nuclei of an isotope to decay, unaffected by chemical or physical conditions
• The Haber process is used to produce the ammonia required for fertiliser production, utilizing nitrogen and hydrogen combined to make ammonia with the help of an iron catalyst to increase reaction rate
• At low temperatures, the forward reaction in the Haber process is too slow to be economical, but increasing the temperature speeds up the reaction, although the backward reaction becomes more dominant
• The Ostwald process uses ammonia, oxygen, and water to produce nitric acid, with a platinum catalyst used in this process at 800°C
• Radioactive decay involves changes in the nuclei of atoms, where unstable nuclei (radioisotopes) can become more stable by emitting alpha, beta, or gamma radiation
• Types of radiation:

  • Alpha particles (α) consist of two protons and two neutrons, have a range of only a few centimeters in air, and are stopped by a piece of paper
  • Beta particles (β) are electrons ejected from the nucleus of an atom, can travel over a meter in air but are stopped by a thin sheet of aluminum
  • Gamma rays (γ) are electromagnetic waves emitted from within the nucleus of an atom, can travel great distances in air, and are stopped by barriers made of materials like lead or concrete
• Nuclear equations are used to show the changes in the nucleus of radioisotopes, ignoring the electrons arranged outside the nucleus
• A chemical cell can be made by joining copper and zinc half-cells, with an ion bridge (salt bridge) linking the half-cells to complete an electrical circuit
• In a cell involving zinc:

  • Half-cell: zinc
  • Half-cell reaction: Zn (s) → Zn²+ + 2e¯
• In a cell involving copper:

  • Half-cell: copper
  • Half-cell reaction: Cu²+ + 2e¯ → Cu
• An ion bridge (salt bridge) can be used to move electrons across the electrical circuit in chemical cells
• Half cells involving non-metals like carbon in iron(III) chloride solution do not conduct electricity
• In a cell involving carbon:

  • Half-cell: carbon
  • Half-cell reaction: Fe³+ + e¯ → Fe²+
• Additional polymerization:

  • Monomer: ethene
  • Repeating unit: -CH2-
• Metal ores have been extracted for thousands of years, with the ease of extraction depending on the metal's reactivity
• Gold is found uncombined in the crust and can be extracted by heating alone
• Methods of metal extraction:

  • Heating with carbon or carbon monoxide (for Cu, Pb, Sn, Fe, and Zn)
  • Electrolysis (for more reactive metals including aluminium)
• During electrolysis, metals are reduced, which is the decomposition of an ionic compound into elements using electricity
• An electrochemical cell can be made by placing metals in an electrolyte where electrons flow through wires, with the further apart elements in the electrochemical series producing a greater voltage when used in the cell
• Plastics belong to a group of materials called polymers
• Polymers are long chain molecules formed by joining together a large number of small molecules called monomers
• Addition polymerisation is a chemical reaction where unsaturated monomers are joined, forming a polymer
• During addition polymerisation, when monomers are mixed in the presence of a catalyst, one of the covalent bonds in the C=C bond breaks, allowing monomer molecules to join together in a chain
• A repeating unit in a polymer chain is the shortest section that, if repeated, would yield the complete polymer chain (except for the end-groups)