Here's why:

* Valence Electrons: Alkali metals are in Group 1 of the periodic table. This means they have one valence electron in their outermost shell.

* Octet Rule: The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight electrons in their outermost shell.

* Losing an Electron: By losing their single valence electron, alkali metals achieve the electron configuration of the noble gas in the previous period. This configuration has a full octet in the outermost shell, making the atom stable.

Example: Sodium (Na) has one valence electron. When it loses this electron, it becomes a positively charged ion (Na+) with the same electron configuration as the noble gas neon (Ne), which has a full octet.