Here is a video showing the periodic nature of elements. The Alkali Metals of group 1 on the Periodic Table, have the same number of valence electrons. These are the electrons located in the outer most energy levels of the atoms. For Alkali Metals this would be 1. This also makes them highly reactive, as it is not difficult for them to lose 1 electron to water. This process creates Hydroxide and Hydrogen gas. Hydrogen gas is quite explosive. Just watch and see.
They all have similar, yet increasing reactive, chemical properties due to this valence electron similarity.
