Group 7: Reactivity & Electronic Configurations (Edexcel GCSE Chemistry: Combined Science)

• When halogen atoms gain an electron during reactions, they form -1 ions called halide ions
• We can use electronic configuration to explain the trends in chemical reactivity down group 7

The atoms of the elements of group 7 all have 7 electrons in their outer shell

• Reactivity of group 7 non-metals decreases as you go down the group
  • As you go down group 7, the number of shells of electrons increases, the same as with all other groups

• However, halogen atoms form negative ions when they gain an electron to obtain a full outer shell
  • This means that the increased distance from the outer shell to the nucleus as you go down a group makes the halogens become less reactive

• Fluorine is the smallest halogen, which means its outermost shell is the closest to the positive nucleus of all the halogen
  • Therefore, the ability to attract an electron is strongest in fluorine making it the most reactive
  • As you move down the group, the forces of attraction between the nucleus and the outermost shell decreases
  • This makes it harder for the atoms to gain electrons as you descend the group
  • Therefore, the halogens are less reactive the further down the group you go