Question

What are alkali metal? Though hydrogen is placed in the alkali metals in modern periodic table, why is not included in alkali metals

Answer 1

Alkali metals are those metals which belongs to group 1 of the periodic table. It includes elements lithium, sodium, potassium, rubidium, caesium, and francium. They are very reactive metals. These metals have only one electron in their outer shell.

Hydrogen is not included in alkali metals because it resembles both alkali metals group 1 and halogens group 17.
Like alkali metals it loses one electron to form a uni-positive ion but unlike alkali metals it doesn't posses metallic character. Like halogens it forms diatomic molecule and covalent compounds but it's reactivity is very low as compared to halogens.