Question

What monatomic ions do potassium (Z = 19) and iodine (Z = 53) form?

Short answer

Potassium forms a cation, i.e.${\mathbf{K}}^{\mathbf{+}}$whereas iodine forms an anion i.e.${\mathbf{I}}^{\mathbf{‐}}$.

Step-by-step solution

Formation of potassium ions

Alkali metals are the metals present in Group . Using the periodic table, the elements in this group are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). These electropositive metals lose one electron quickly (as there is only one electron in their valence shell and on losing this they achieve noble gas configuration) to generate monoatomic ions with a +1 charge on them. Hence, potassium produces a${\mathbf{K}}^{\mathbf{+}}$cation.

Formation of iodide ions

Theelements in Group (also called halogens) are nonmetals. The halogen elements on the modern periodic table are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are electronegative in nature. So, these nonmetals gain one electron rapidly(as there are seven electrons in their valence shell and on accepting one electron from some metal they achieve noble gas configuration) to generate mono-anions with a -1 charge on them. Therefore, iodine produces a anion.