1. Which elements react fastest? To answer this question we need to think what reacting means and why atoms react. Atom want a stable electron configuration and want to be isoelectric with noble gases. (They all want full outside shells) The atoms that react fastest are the ones which can achieve the noble gas configuration fastest.

2. There are two different ways to achieve this configuration: An atom can give away electrons and form positive ions An atom can gain electrons to fill its outer shell this means it forms negative ions

4. Comparing group 1 and group 2

5. Comparing group 16 and group 17

6. So group 1 can achieve their goal, of giving away electrons, more quickly than elements in group 2 and Group 17 can achieve their goal, of gaining electrons, more quickly than elements in group 16

7. Compare the attraction of the outer most electron in Lithium with the that in Sodium Lithium Sodium Sodiums electron also suffers more repulsion from the two layers of inner electrons Lithiums outer electron feels more attraction because it is closer to the nucleus

8. So it is easier for sodium to lose it’s outside electron, because the outer electron of lithium is more attracted to the nucleus and requires more energy to be pulled away from this positive nucleus So how attracted an electron is to the nucleus depends on the distance that it is from the nucleus

9. This is also true for halogens The closer to the nucleus the more attracted an electron is.