Explain why the reactivity of group 1 metals increases as you go down the group.

The reactivity of Group 1 metals, also known as alkali metals, increases as you go down the group due to the following reasons:

1. Atomic Size: As you move down the group, the atomic size increases. This is because each subsequent element in the group has an additional electron shell compared to the one before it.

2. Electron Shielding: With each additional electron shell, there is an increase in electron shielding. This means that the positive charge from the nucleus has a weaker hold on the outermost electrons.

3. Ionization Energy: As a result of the increased atomic size and electron shielding, the ionization energy decreases. Ionization energy is the energy required to remove an electron from an atom. The weaker the hold on the outermost electron, the less energy is required to remove it.

4. Reactivity: Alkali metals react by losing their outermost electron to achieve a stable electron configuration. Therefore, the easier it is to lose this electron (i.e., the lower the ionization energy), the more reactive the element is.

So, as you go down Group 1, the atomic size increases, electron shielding increases, ionization energy decreases, and thus reactivity increases.