Alkaline Earth Metals

The second column on the periodic table of the chemical elements is collectively called the alkaline earth metal group: beryllium, magnesium, calcium, strontium, barium, and radium. Because the outer electron structure in all of these elements is similar, they all have somewhat similar chemical and physical properties. All are shiny, fairly soft—although harder than the alkali metals—and most are white or silvery colored. The steady increase in melting and boiling points with increasing molecular mass noticed in the alkali metal group is less pronounced in the alkaline earths; beryllium has the highest rather than the lowest melting point, for example, and the other metals do not follow a consistent pattern. All the alkaline earth metals react with water to produce hydrogen gas and the metal hydroxide, although somewhat less vigorously than the alkali metals. Magnesium metal can be set on fire, and burns with an extremely intense white light as it combines with oxygen in the air to form magnesium oxide. Strontium, barium, and calcium react readily with oxygen in the air to form their oxides.

Alkaline earth metals almost always form ions with a positive (+2) charge, and are sufficiently reactive as elements so they usually occur in nature only in compound form, frequently as carbonates or sulfates. Calcium is by far the most abundant, followed by magnesium, and then in much lesser amounts barium, strontium, and beryllium. Radium is radioactive and fairly rare; what exists in the earth's crust occurs almost exclusively in uranium deposits.

Several of the alkaline earth metals glow with a characteristic color when placed in a flame; calcium gives off an orange light, strontium a very bright red, and barium an apple green. These flame tests are useful for identifying the metals. Strontium compounds are often added to fireworks displays to obtain the most vivid reds.