Alkaline earth metal, or alkali earth metal, is any chemical element from the second column of the periodic table. In order of atomic number, the alkaline earth metals are beryllium (atomic number, 4), magnesium (12), calcium (20), strontium (38), barium (56), and radium (88). All of these elements are found naturally in Earth’s crust as a compound with other elements. All of them are stable in nature except radium, which is radioactive. The group takes its name from the fact that its elements were first well known from their oxides (compounds with oxygen), historically called “earths.” Most earths combine with water to make alkaline (acid-neutralizing) solutions.
The alkaline earth metals show typical metallic properties. For example, they appear silvery and shiny and conduct heat and electric current well. They react chemically with nonmetals, losing two electrons to form ions with a 2+ charge. All of them but beryllium react with water.
Magnesium and calcium are essential for life. Beryllium, barium, and radium are toxic to most living things, but some compounds are used in a variety of helpful ways. Strontium has no known natural function in the body, but it can become incorporated into bones in place of calcium. This can lead to serious health problems in the case of strontium-90, a radioactive isotope (form) of strontium, created in nuclear explosions.
Magnesium is the alkaline earth metal that is produced industrially in the greatest amounts. Many metal alloys (mixtures) incorporate magnesium. Also, it burns brightly in air and is thus used in fireworks, flares, and tracer bullets. Calcium compounds are also widely used in industry and agriculture. Calcium oxide, called lime or quicklime, is a crucial part of cement.
