periodicity

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  • periodicity (period 3)
    • s block, p block and d block
    • 1st IE: energy required to remove 1 mol of e- from 1 mol of gaseous atom to form 1 mol of +1 ions
    • atomic radius decreases across a period
      • proton number increases so nuclear charge increases
        • more attraction between nucleus and outer e-
      • similar shielding
    • 1st IE generally incenses
      • increasing protons
        • more attraction between outer e- and nucleus
      • exceptions
        • Mg and Al
          • 3p orbital is slightly further from 3s and has additional sheilding
        • P to S
          • 3p e- in P are all unpaired
          • in S 2 e- are paired
            • more repulsion
    • melting point varies
      • Na to Al
        • melting points increase
          • number outer e- increase so more can be delocalised
            • greater attraction between (+) ions and delocalised e-
      • silicon melting point is high
        • giant covalent structure
          • lots of energy needed to overcome the covalent bonds
      • argon is low
        • its an atom
          • little energy needed to break weak VDWs
      • P4, S8 and Cl2
        • molecular with VDWs
          • bigger molecules have stronger VDWs so suffer is the highest and chlorine is the lowest

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