Chem chap 7

    Cards (17)

    • Periodic table arrangement:

      • by increasing atomic number
      • in periods - by periodicity ( repeating trends in physical and chemical properties)
      • in groups - by similar chemical properties
    • history of periodic table
      • before, elements were ordered by atomic mass
      • Mendeleev created the periodic table - he left gaps for undiscovered elements
      • he grouped them in similar chemical properties
      • now the periodic table is ordered by proton number
    • Factors that affect ionisation energy:
      • nuclear charge
      • atomic radius
      • electron shielding
    • What is first ionisation energy?
      The energy required to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
    • trend of first ionisation energy down a group?
      decreases down a group, because:
      • nuclear charge increases - this is not enough to increase ionisation energy
      • atomic radius increases - attractive force between nucleus and outer electrons is weaker - energy required to remove an electron decreases
      • electron shielding increases - more shells between nucleus and outer shell - attractive force is weaker - energy required to remove an electron decreases
    • What do ionisation trends down a group support?
      • support the Bohr model of the atom
    • trend of first ionisation energy across period 2 and 3?
      • increases, because:
      • nuclear charge increases - attractive force increases - more energy required to remove an electron
      • atomic radius decreases (due to increased nuclear charge) - attractive force increases - more energy required to remove an electron
      • electron shielding remains constant
    • what is the cause of the slight first decrease of ionisation energy across periods 2 and 3?

      • this happens because of an addition of an electron
      • the elements sit at a subshell which is slightly further from the nucleus
      • attractive force decreases - energy required to take an electron decreases
    • What is the cause of the second slight decrease of the ionisation energies in p2 and p3?
      • electron repulsion
      • removing an electron from sulphur/oxygen involves taking it from an orbital with 2 electrons
      • electrons repel each other - less energy needed to remove an electron from an orbital with 2 than in 1 (in nitrogen and phosphorous)
    • successive ionisation?

      The removal of more than 1 electron from the same atom
    • what is metallic bonding?
      strong electrostatic attraction between cations and delocalised electrons
    • what structure are metals?
      giant metallic lattice structure
    • Describe graphite
      • each carbon bonded 3 times, 4th electron delocalised
      • strong covalent bonds - very high melting point and insoluble
      • layers far apart - low density
      • delocalised electrons between layers carry a charge - conduct electricity
      • weak forces between layers - layers slide over each other easily
    • describe diamond/silicon ?
      • each carbon bonded 4 times in tetrahedral shape
      • very strong covalent bonds - very high melting point, strong, insoluble
      • compact, rigid structure - thermal conductor
      • no delocalised electrons - not an electrical conductor
      • can be cut to make gemstones
    • desribe graphite?

      • is 1 layer of hexagonal carbon rings
      • one layer thick - lightweight, transparent
      • has delocalised electrons - conductor of electricity, also they strengthen the covalent bonds - high strength
    • trend in melting points across p2 and p3?
      1
    • What are dicots?
      Plants which
      • produce seeds which contain two cotyledons, which act as food stores for the developing embryo
      • form the first embryonic leaves when the seed germinates
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