Why is potassium more reactive than sodium?

The reactivity of group 1 elements increases as you go down the group because the atoms become larger; the outer electron becomes further from the nucleus; the force of attraction between the nucleus and the outer electron decreases; the outer electron is lost more easily.

This is todo with the structure of the atoms. Both are in Group 1 of the periodic table so have one valence (outer) electron which is relatively easy to lose due to a factor known as shielding (I can add more detail here if needed) and the desire to acquire a ‘noble gas configuration’. As potassium is larger than sodium, potassium’s valence electron is at a greater distance from the attractive nucleus and is so removed more easily than sodium’s valence electron. As it is removed more easily, it requires less energy, and can be said to be more reactive.