The organization of elements into groups on the periodic table reflects a deep connection between atomic structure and chemical behavior. Elements within the same column, or group, share remarkably similar properties because they possess the same number of valence electrons in their outermost shell. These valence electrons are the primary drivers of chemical reactions and bonding, establishing the characteristic traits of an entire group. The Alkaline Earth Metals are one such family, representing the second column on the periodic table.
Identification and Location on the Periodic Table
The Alkaline Earth Metals constitute Group 2 of the periodic table, sometimes referred to by the older designation of IIA. This group includes six elements: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and the radioactive element Radium (Ra). Every element in this group is defined by having two valence electrons in its outermost s-orbital, which dictates their shared chemical personality.
The name “Alkaline Earth Metal” is derived from two historical observations about their compounds. The term “earth” was historically applied to non-metallic substances that were insoluble in water and highly resistant to heating. The “alkaline” part comes from the fact that their oxides, such as calcium oxide, react with water to form basic solutions, known as alkalies.
Defining Physical and Chemical Properties
These elements are all silvery-white, lustrous metals that are relatively soft, though they are noticeably harder and denser than the Alkali Metals. They are not found in their pure form in nature because they are highly reactive. This reactivity stems from the ease with which they shed their two valence electrons to achieve a stable, noble gas electron configuration.
The loss of these two electrons results in the formation of a cation with a stable +2 oxidation state in nearly all their compounds. This tendency makes them strong reducing agents in chemical reactions. Reactivity increases as one moves down the group from Beryllium to Radium, a trend linked to the increasing atomic radius. As the atoms get larger, the valence electrons are farther from the positive pull of the nucleus, making them easier to remove.
Beryllium is an exception within the group; its small size and high charge density cause its compounds to exhibit more covalent character, deviating from the ionic nature of the heavier members. The elements exhibit relatively low densities compared to most other metals, though density increases with atomic number. When exposed to air, the metals readily tarnish as they react with oxygen to form a thin surface layer of the metal oxide.
Essential Applications and Biological Roles
The Alkaline Earth Metals are economically and biologically important elements, especially the lighter members. Calcium is the most abundant of the group in the human body, with a majority incorporated into the structure of bones and teeth. Beyond structural support, calcium ions are instrumental in transmitting nerve impulses, facilitating muscle contraction, and enabling blood clotting.
Magnesium plays an important role in biology by acting as an essential cofactor for hundreds of enzymes. It is also the central atom in the chlorophyll molecule, making it indispensable for photosynthesis in plants. Industrially, magnesium is frequently alloyed with aluminum to create strong, lightweight materials used in manufacturing aircraft and aerospace applications.
Beryllium, due to its low density and high strength, is primarily used to form specialized alloys with copper, valued for their stiffness and electrical conductivity in components like high-strength springs. Barium compounds, particularly barium sulfate, are widely used in medical settings. Barium sulfate is administered orally for X-ray imaging of the digestive tract because it is opaque to X-rays. The heaviest member, Radium, is highly radioactive and was historically used in cancer therapy to destroy malignant cells.