Trends

• Group 1 elements


  Get more reactive going down the group
• Group 1 elements


  • Li
  • Na
  • Rb
  • Cs
• Group 7 elements


  Get less reactive going down the group
• Group 7 elements


  • Cl
  • Br
  • At
• You can explain these trends by looking at the electronic structures and how the atoms tend to lose or gain electrons in their reactions
• Reactivity within groups


  • As you go down a group in the periodic table, the number of shells occupied by electrons increases, by one extra electron shell per period
  • Atoms become larger going down any group
• Larger atoms


  Lose electrons more easily going down a group
• Larger atoms


  Gain electrons less easily going down a group
• Atoms of alkali metals tend to lose electrons when they form chemical bonds
• Atoms of the halogens tend to gain electrons
• The size of the positive charge on the nucleus


  Becomes larger as you go down a group, as more protons are present inside the nucleus
• The increasing nuclear charge

  Suggests that the attraction for the outer electron should get stronger
• The greater distance and the shielding effect of inner electrons


  Outweigh the increasing nuclear charge
• The change from Li to Li+

  Takes more energy than Na changing to Na+, shielded by more inner shells of electrons than lithium's outer electron
• In Group 1, the outer electron


  Gets easier to remove going down the group and the elements get more and more reactive
• Reactivity decreases going down Group 7
• Factors to explain the trend in Group 7

  • The size of the atom
  • The shielding effect of inner electrons
  • The nuclear charge
• When Group 7 elements react, their atoms

  Gain an electron in their outermost shell (highest energy level)
• Going down the group, the outermost shell's electrons


  Get further away from the attractive force of the nucleus, so it is harder to attract and gain an extra incoming electron
• The outer shell


  Will also be shielded by more inner shells of electrons, again reducing the electrostatic attraction of the nucleus for an incoming electron
• The effect of the increased nuclear charge going down the group

  Is outweighed by the effect of increased distance and shielding by more inner electrons
• Chlorine is less reactive than fluorine


  The attraction for the incoming electron when F changes to F- is much greater than when Cl changes to Cl-