The Periodic Table - Periods and Groups

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Trends across a period

  • The ionisation energy shows a general increase across each period
  • There is abig decrease after each noble gasbecause: new shell; more shielding; greater distance from nucleus to outer shell


 Generally across a period:

  • Number of protons increases, so more attraction acting on electrons
  • Electrons are being added to the same shell - the outer shell is drawn in slightly, decreasing the atomic radius
  • Electron shielding will not change
  • Nuclear charge increases
  • Greater attraction
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Trends down a group

  • The first ionisation energy shows a general decrease down a group


Generally down a group:

  • Number of shells increases, so the distance from the nucleus to outer electrons increases (so a weaker force of nuclear attraction)
  • More inner shells - increased shielding
  • The atomic radius increases because there is less attraction so the electrons are not pulled as close to the nucleus
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Trends down Group 2

  • Solubility and alkalinity increases down the group
  • Reactivity increases down the group - this reflects the increased ease of losing the outer electrons (vigorous reaction with water increases down the group due to the trends shown down a group)
  • Ease of thermal decomposition decreases as you go down the group
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Trends down Group 7

  • Boiling point increases down the group because as you move down the number of electrons increases, leading to an increase in van der Waals forces between molecules
  • Reactivity decreases down the group - due to the trends shown down a group
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