The alkali metals, situated in group 1 of the periodic table, are all soft, silvery-white metals with low melting points. The melting points fall as we go down the group, ranging from 180.6 degrees Celsius for lithium to about 27 degrees Celsius for francium.
All of the metals have a single electron in their outermost shell, and the ease with which this electron engages in bonding helps to explain their great reactivity. Reacting easily with oxygen, they tarnish rapidly on exposure to air, and all react violently with water (this results in alkaline solutions, hence the group name). They readily form compounds with the halogens, and are so reactive that they are never found free in nature. Because of the ease with which they give up their outermost electron, they are very efficient reducing agents.
The metals are excellent conductors of heat and of electricity, and because their flames have characteristic colours, it is possible to identify the elements with a flame test. Lithium gives a crimson flame, sodium a yellow, potassium a violet, rubidium a reddish-violet, and caesium a blue.
The properties of francium, a radioactive element with a longest half-life of 22 minutes, are difficult to determine.
