After the third energy level has 8 electrons, the next electron goes into the fourth level. 4th Period: Potassium and Calcium—Electrons go into the fourth energy level. A small piece of sodium metal ...

Moist air reacts with potassium to form potassium oxide. This creates a layer over the surface of the metal. These observations show that the reactivity of these metals increases going down the group.

Potassium reacts quickly with water producing a lilac-coloured flame For example, when potassium is added to water, the metal melts and floats. It moves around very quickly on the surface of the ...