Alkaline earth metals are shiny, soft or semi-soft metals that are insoluble in water. They are generally harder and less reactive than the metals in in group IA, such as sodium, and are softer and more reactive than the metals in group IIIA, such as aluminum. When they combine with oxides (molecules of oxygen plus another element) they make up some of the most common minerals on Earth, with a variety of uses in industry, medicine and consumer goods. Some compounds give off a great deal of light when heated, making them key ingredients in fireworks.
Chemistry of Group IIA
In compounds, alkaline earth metals lose two electrons, forming ions with a 2+ charge. They readily react with oxygen, which accepts electrons to form ions with a 2- charge. The positive and negative ions are attracted to each other, resulting in a bond that has a net charge of 0. The resulting compounds are called oxides. Solutions made from these oxides and water are bases with a pH greater than 7. The alkaline nature of these solutions provides this group of metals with its name. Alkaline earth metals are highly reactive, and the activity of these metals increases moving down the group. Calcium, strontium and barium can react with water at room temperature.
In its elemental form, beryllium is a soft metal, silvery white in color. Ore compounds containing beryllium, aluminum and silicon can form green and bluish-colored gemstones such as emeralds, aquamarine and alexandrite. Beryllium is useful in radiology because X-rays can pass through beryllium, making it appear transparent. It is often used to make X-ray tubes and windows. Beryllium increases the hardness of alloys that are used to make tools and watch springs.
The physical properties of magnesium are similar to beryllium. It doesn’t react with water at room temperature, but readily reacts with acids. Magnesium is one of the most plentiful elements found in the Earth’s crust and is a key component in chlorophyll, the substance in green plants used in photosynthesis. Magnesium is useful in healthcare as it is one of the main ingredients in antacids, laxative and Epsom salts. Combustion of magnesium yields a bright, white, long-lasting flame, making it useful in fireworks and flares.
Calcium is even more plentiful on Earth than magnesium. The silvery, semi-soft metal easily forms compounds with both oxygen molecules and water. In nature it is typically found as calcium carbonate, or limestone. Calcium is a key component in the structures of living things including bones, teeth, shells and exoskeletons. Calcium is also an important substance for manmade structures because it is used to make plaster, cement, drywall and other building materials.
Shiny and soft, strontium forms compounds with oxygen and other oxides such as carbonate (CO3), nitrate (NO3), sulfate (SO4) and chlorate (ClO3). Salts derived from strontium compounds burn red and are used in fireworks and signal flares.
Unlike the transparency of beryllium, X-rays cannot penetrate barium. Barium sulfate is commonly used to aid in using X-rays to detect problems in the digestive tract. This compound is insoluble in water and coats the esophagus, stomach and intestines when swallowed. Barium nitrate and barium chlorate are used in fireworks to give off green light when heated. Barium is also an ingredient in paint pigments.
Radium is white in color and soft and shiny like the other alkaline earth metals. However, its radioactivity sets it apart from the rest of its group. Soon after its discovery by the Curies in the late 1800s, radium was used for medical therapies and to make glow-in-the-dark clocks and watches. Decades later the use of radium ceased when people discovered the dangers of radiation. Today radium is used in the treatment of certain types of cancers.