Why are halogens and alkali metals likely to form ions

To achieve the stable noble gas configuration

Explanation:

According to the octet rule, chemical elements tend to bond in order to complete their valence shell and attain the stable noble gas configuration: ns² np⁶. Thus elements tend to lose, share or gain electrons to have eight electrons in their valence shell.

Alkali metals are the reactive chemical elements that belong to the group 1 of the periodic table. The general electron configuration of alkali metals is ns¹.

So alkali metals tend to lose the valence electron to form a monovalent cation or positively charged ion and achieve the stable noble gas configuration.

Halogens are the reactive chemical elements that belong to the group 17 of the periodic table. The general electron configuration of halogens is ns² np⁵.

So halogens tend to gain one electron to form a monovalent anion or negatively charged ion and achieve the stable noble gas configuration.

Therefore, halogens and alkali metals are the reactive elements that tend to lose one valence electron and gain one electron, respectively, to form ions and achieve the stable noble gas configuration.