Explain why the reactivity increases as you go down group1, but decreases as you go down in group 7. (4 marks)

The reactivity in group 1 increases as you go down the series because the electrostatic force of attraction between the further electron and the nucleus gets weaker as the atom size increases, meaning the electron can be lost easily, making it react. However, in Halogens, the reactivity would decrease as you go down the series because the electrostatic force between the outer electron and the nucleus weakens due to a larger atom size. This would make it harder for the atom to gain an electron and react.