Early Periodic Table

early 19th century less than 40 elements discovered
1. new ones discovered regularly
  1. scientists noticed patterns in the way they reacted- the properties
    1. eg atomic weight
John Newlands
1. order of atomic mass
2. law of octaves
  1. similar properties every 8th element
  2. Problems
    1. some groups have a mix of metals and non metals
    2. only worked for first few elements (broke after calcium)
    3. elements still being discovered
Demitri Mendeleev
1. left gaps for undiscovered elements- so elements could have similar properties to others in the group
  1. predicted atmoic masses and properties for undiscovered elements
After Mendeleev
1. noble gases discovered
2. electrons discovered
3. atomic structure discovered
4. in accuracies that still existed solved by placement in order of atmic number
5. Modern periodic table --- groups and periods
Modern Periodic Table
1. Now by atmoic number
2. period number is number of outermost shell
3. group number is the number of electrons on outermost shell
4. Group 1 - Alkali Metals
  1. low density
  2. react with non mdetals to form ionic compounds
  3. react with water to release hydrogen
  4. form hydroxides that dissolvve in water to give alkaline solutions
  5. futher down the group - more reactive the element + lower melting & boiling point
  6. soft
  7. conduct heat and electricity
  8. low density-float on water
  9. react with water and oxygen in air (which is why it tarnishes quick)
    1. stopped by being stored in oil
  10. when they react lose electron an form +1 ions
  11. alkali metal+water= metal hydroxide +hydrogen
  12. going down the group ----( high up the group) outer electron closer to nucleus so stronger attraction to nucleus so less screening by inner electrons thus electron lost less easily.......lower down the outer electron is futher from nuclues so nuclear attraction weaker so more screening by inner electron thus electron lost more easily
    1. higher energy level of outer electron - the more easily the electrons are lost and the less easily the electrons are gained
  13. Group 7 - Halogens
    1. poor conductors
    2. poisonous non metals - coloured vapours
    3. react with metals to form ionic compounds
    4. ion produced called halide and has charge of -1
    5. further down --- less reactive.....higher melting & boiling points due to weak molecules
    6. A more reactive halogen can displace less reactive halogen from an aqueous solution of its salts ( dissolved in water)
      1. eg Cl 2 + 2KBr = 2KCl + Br 2
    7. dont conduct heat or electricity
    8. diatomic molecules
    9. going down the group----( high up) outer electron closer to nucleus so nuclear attraction stronger so less screening by inner electrons thus electron gainedd more easily (lower down) outermost electron futher from nucleus so weaker nuclear attraction so more screeening by inner electrons thus electron gained less easily
      1. higher energy level of outer electron ---- electron more easily lost....electron less easily gained
    10. Transition Metals
      1. higher melting and boiling points (except mercury a liquid at room temp)
      2. harder and stronger - good for structrual material eg construction,wiring
        less reactive so dont react with water and oxygen
      3. form ions with different charges eg Fe+2 or Fe+3
      4. form coloured compounds
      5. useful as catalysts
      6. between group 2 and 3

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