Why do alkali metals have only one electron in their outer shell?

Alkali metals have only one electron in their outer shell because they belong to Group 1 of the periodic table.

Alkali metals, which include lithium, sodium, potassium, rubidium, caesium, and francium, are all found in Group 1 of the periodic table. The group number of an element in the periodic table corresponds to the number of electrons in its outer shell, also known as its valence shell. Therefore, as alkali metals are in Group 1, they each have one electron in their outer shell.

This single electron in the outer shell is significant as it greatly influences the chemical properties of alkali metals. Electrons in the outer shell are involved in chemical reactions, and having only one electron makes alkali metals highly reactive. This is because they tend to lose this single electron in order to achieve a stable electron configuration, which usually means having a full outer shell. This loss of an electron forms a positive ion, as the atom now has one more proton than it has electrons.

The reactivity of alkali metals increases down the group. This is because as you go down the group, the outer electron is further from the nucleus and is therefore less attracted to it. This makes it easier for the electron to be lost in a chemical reaction, increasing the reactivity of the metal.

In summary, alkali metals have only one electron in their outer shell due to their position in Group 1 of the periodic table. This single electron plays a crucial role in determining the chemical properties and reactivity of these metals.