Why does potassium react more readily in water than sodium?

Both potassium and sodium are in the same group on the periodic table, but have a different atomic structure. Sodium has three outer electron rings, while potassium has 4. Both atoms only have one electron on the outermost ring. However, as potassium has one extra ring in between the nucleus and outer ring and the distance to the outer electron is greater, the force that the nucleus exerts on the outermost electron is smaller.This outer electron is therefore lost more easily in potassium (can be quantified in the value of 1st ionisation energy - energy needed to remove the first electron from the outer shell).