The most reactive metals found on the periodic table are the alkali metals, which are lithium, sodium, potassium, rubidium, caesium and francium. The alkali metals are found on the periodic table's s-block, because the outermost electron in these elements is in an s-orbital.
Because these elements are so reactive, they do not occur freely in nature. This is because all of these metals have only a single electron in their outer shell, and they lose it to other elements during ionic bonding. In order to prevent reaction with air, alkali metals must be stored in oil. In nature, the elements are mainly found in salts.
Like all metals, alkali metals are shiny, malleable, ductile and good conductors of heat and electricity, but alkali metals are softer than most other metals. In fact, they are so soft that they can easily be cut with a knife. When cut, a shiny surface is exposed, but it rapidly tarnishes due to oxidation.
Alkali metals can be used in many different ways. Both sodium and potassium are essential dietary elements, and table salt, or sodium chloride, has been used by people since ancient times. One of the most well known uses of these metals in their purest form is the use of rubidium and caesium in atomic clocks. Caesium atomic clocks are the most precise representation of time available today.