Question

Why potassium is most reactive in reactivity series

Answer 1

    Potassium belongs to Group 1 metals in the Periodic table. They are very reactive metals. They contain in their electronic configuration 1 lone electron in the s orbital of the outermost shell.

    K = Potassium :  1s2  2s2  2p6  3s2  3p6  3s1 

   Potassium achieves the most stable configuration (ideal gas config) by losing an electron. So it is very reactive and becomes a K+ ions easily.  Potassium is more reactive than Sodium and Lithium because Potassium is bigger than them.  So outermost electron is farther away from nucleus. So the ionization energy in K is less than that in Na or in Li.

   So Potassium is more reactive than many other metals. However, Rubidium Rb and Cesium Cs are more reactive than Potassium. They are below Potassium in Group 1.  But they are not commonly used metals.  So we do not include them when we say potassium is most reactive.  However they are bigger than Potassium and so are more ready than K to lose electrons.

   In group 2, the alkali metals have two electrons in s orbitals. They are paired. So the ionization energy is more than that of the Group 1 metals. Hence potassium is high in the reactivity series higher than group 2 metals.

Answer 2

Potassium is in the most reactive group of elements, the alkali metals, but it's not the most reactive metal within the group.

The alkali metals, Group 1A, are the most reactive metals because they have one valence or outer electron. They lose this electron very easily, forming ions with a charge of +1. Within the alkali metals family, reactivity increases with increasing atomic number. This makes Francium the most reactive, followed by cesium, rubidium, potassium, sodium and lithium. Francium is almost non-existent in nature so cesium is the most reactive metal of those observed.

The reason for the trend of increasing reactivity with increasing atomic number within the alkali metals family has to do with the increasing number of electrons. Each element going down has an additional full electron energy level. Inner electrons repel the outer valence electron, making is less attracted to the nucleus and easier to remove. Francium is the largest atom within the group and has the least attraction between its valence electron and the nucleus so it loses an electron more easily than the other alkali metals. This same strong reactivity because of one valence electron is true of potassium, as well.