Alkali
In chemistry, an alkali (; from Arabic: "al-qaly" "ashes of the saltwort") is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Alkali metal
Hydrogen, like the alkali metals, has one valence electron and reacts easily with the halogens, but the similarities end there because of the small size of a bare proton H compared to the alkali metal cations. Its placement above lithium is primarily due to its electron configuration. It is sometimes placed above carbon due to their similar electronegativities or fluorine due to their similar chemical properties.