Physical Properties

The alkaline earth metals are, broadly speaking, silvery-white, lustrous and relatively soft — though noticeably harder than the alkali metals of the same period; beryllium and magnesium have a slightly greyer cast than the rest. Their smaller atomic size compared with the alkali metals gives them higher melting and boiling points too, though the trend down the group itself is not perfectly systematic. Because ionization enthalpy is still low, all of them remain strongly electropositive, and this electropositive character actually increases from Be to Ba.

Three of the heavier members give characteristic flame colours — calcium brick-red, strontium crimson and barium apple-green — as their outer electrons are kicked to a higher level by the flame's heat and drop back releasing visible light; beryllium and magnesium do not show this effect because their electrons are held too tightly to be excited by an ordinary flame. The Ca/Sr/Ba flame test, like the alkali-metal one, is a standard qualitative-analysis tool and the basis of flame photometry. Like the alkali metals, all of Group 2 conduct heat and electricity well — a typical metallic property.

Table 10.2 — Atomic and Physical Properties of the Alkaline Earth Metals