- The alkaline earth metals form Group 2 of the periodic table and consist of six elements: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
- These elements are called “alkaline earth metals” because their oxides and hydroxides are alkaline (basic) in nature and were historically found in the earth’s crust.
- They are all shiny, silvery-white metals and share many chemical properties due to their similar electronic configurations, each having two valence electrons in the outermost s-orbital (ns²). This configuration gives them a stable tendency to form +2 cations by losing these electrons during chemical reactions.
- In terms of physical properties, alkaline earth metals are relatively soft but harder than the alkali metals of Group 1. They possess higher densities and melting points compared to alkali metals, though these values decrease somewhat down the group. They are also good conductors of heat and electricity. The metallic character increases as we move down the group: beryllium behaves more like a metalloid in its reactivity, while radium is highly reactive. Their atomic size increases down the group due to the addition of electron shells, while ionization energy decreases, making the heavier members more reactive.
- The chemical properties of alkaline earth metals are dominated by their reactivity with nonmetals and water. They readily react with oxygen to form basic oxides (such as CaO, quicklime), which further react with water to form hydroxides (alkaline in nature, hence the name). For example, calcium reacts with water to form calcium hydroxide and hydrogen gas. Their reactivity increases down the group; beryllium is resistant to reaction with water due to a strong oxide layer, while barium and radium react vigorously. They also form ionic compounds with halogens (such as CaCl₂ and BaCl₂), sulfates, and carbonates. Many of their compounds are sparingly soluble in water, with solubility generally increasing down the group.
- Each member of this group plays a significant role in biological and industrial processes. Magnesium is essential for plant life, as it forms the central atom in chlorophyll molecules, which drive photosynthesis. It is also widely used in alloys due to its light weight. Calcium is vital for animals, forming the structural basis of bones and teeth as calcium phosphate. Industrially, calcium compounds like lime (CaO) and limestone (CaCO₃) are fundamental in cement, construction, and steel-making. Strontium is used in fireworks to produce bright red colors, while barium finds use in contrast imaging for X-ray diagnostics, as barium sulfate is opaque to radiation. Radium, once used in luminous paints, is radioactive and now mainly of historical importance, though it helped pioneer studies of radioactivity.
- Overall, the alkaline earth metals are characterized by their trends in reactivity, their formation of stable ionic compounds, and their significant roles in both natural processes and human technology. From the strengthening of bones to the construction of buildings and the production of light alloys, these elements remain crucial to both life and industry.
