ALKALI METAL

Properties
The alkali metals exhibit many of the physical properties common to metals, although their densities are lower than those of other metals. Alkali metals have one electron in their outer shell, which is loosely bound. This gives them the largest atomic radii of the elements in their respective periods. Their low ionization energies result in their metallic properties and high reactivities. An alkali metal can easily lose its valence electron to form the univalent cation. Alkali metals have low electronegativities. They react readily with nonmetals, particularly halogens.

Summary of Common Properties
Lower densities than other metals
One loosely bound valence electron
Largest atomic radii in their periods
Low ionization energies
Low electronegativities
Highly reactive