Hydrogen and Alkali Metals: Elements of the First Main Group

Here, all elements of the first main group are united, that is, hydrogen and all alkali metals. Hydrogen was discovered 250 years ago, the metals lithium, sodium, and potassium 200 years ago. Rubidium and cesium followed 50 years later, and francium, whose isotopes are all extremely short-lived, was first described in 1939. Although these elements are mentioned in many publications and are therefore quite well-known, we have an interesting family of elements before us here. The alkali metals are chemically very reactive and show regular gradations of their properties. Thus, from lithium to cesium, density and reactivity increase, while melting and boiling points, as well as electronegativities, decrease. Likewise, there is a violent to explosive reaction with water and mineral acids. In their compounds, they are almost always the electropositive partner.