The periodic table organizes chemical elements into groups (columns) and periods (rows). Group 2, the second column from the left, contains six distinct metallic elements, starting with Beryllium and ending with the radioactive element Radium. These elements are collectively known as the Alkaline Earth Metals.
The Alkaline Earth Metals
The designation “Alkaline Earth Metals” is a historical name describing two fundamental characteristics of this group. Early chemists used the term “earth” for substances that were nonmetallic, insoluble in water, and resistant to heat, properties shared by the naturally occurring oxides of these elements.
The “alkaline” part of the name comes from the fact that the oxides of these metals produce basic, or alkaline, solutions when dissolved in water. The six elements in this group are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).
A defining feature of the Alkaline Earth Metals is their electronic configuration, possessing two valence electrons in the outermost s-orbital (\(ns^2\)). This configuration dictates their chemical behavior across the group. Because these two electrons are relatively easy to remove, all Alkaline Earth Metals almost exclusively exhibit an oxidation state of +2 in their compounds.
Chemical Reactivity and Bonding
The presence of two valence electrons makes the Alkaline Earth Metals highly reactive. The atoms readily lose these two outer electrons to achieve a stable, noble gas configuration, forming a positively charged \(M^{2+}\) ion. This loss of electrons classifies them as strong reducing agents, meaning they readily donate electrons to other elements during chemical reactions.
Their strong tendency to form \(M^{2+}\) ions means they primarily engage in ionic bonding, combining with nonmetals to create crystalline compounds. A steady trend of increasing reactivity is observed moving down the group, from Beryllium to Radium. This is explained by the increasing atomic size and greater shielding of the nucleus, which lowers the ionization energy.
The reaction with water serves as a clear illustration of this reactivity trend. Beryllium exhibits anomalous behavior and is the only element that does not readily react with water or steam. Magnesium resists reaction with cold water but will react with hot water or steam to form its oxide and hydrogen gas.
Moving further down, Calcium, Strontium, and Barium react with cold water, forming the metal hydroxide and hydrogen gas, with the reaction becoming progressively more vigorous. Barium, the heaviest non-radioactive member, is the most reactive of the stable elements and reacts violently with water.
Physical Properties and Practical Uses
The Alkaline Earth Metals share several distinct physical properties, typically appearing as shiny, silvery-white metals with a metallic luster when freshly cut. They are generally denser and harder than the Group 1 Alkali Metals. They also possess moderately higher melting and boiling points than the elements in Group 1.
These elements and their compounds have a wide range of practical applications in both industry and biology. Magnesium, with its low density and high strength, is widely used in lightweight alloys for aerospace and automotive industries. Biologically, Magnesium is a component in the chlorophyll molecule used by plants for photosynthesis.
Calcium serves as a fundamental component of bones and teeth in vertebrates. Its compounds are also widely used in construction; calcium carbonate is the main ingredient in limestone, and calcium oxide (lime) is utilized in cement and mortar. Strontium compounds are known for producing the bright red color in fireworks and flares.
Barium compounds, which are dense and opaque to X-rays, are used in medical imaging procedures like the “barium swallow” to visualize the gastrointestinal tract. Radium, the heaviest element in the group, is intensely radioactive and was historically used in glow-in-the-dark paints due to its luminescence. Radium is now primarily used in cancer treatments.